{"id":98252,"date":"2026-08-31T14:56:51","date_gmt":"2026-08-31T06:56:51","guid":{"rendered":"https:\/\/www.wsisp.com\/helps\/98252.html"},"modified":"2026-08-31T14:56:51","modified_gmt":"2026-08-31T06:56:51","slug":"%e5%88%ab%e5%86%8d%e6%80%aa-et-%e6%a8%a1%e5%bc%8f%e6%bc%8f%e4%ba%8b%e4%bb%b6%e4%ba%86%ef%bc%81%e6%b7%b1%e6%8c%96-c-%e6%8e%a5%e5%85%a5%e7%bd%91%e5%85%b3-close_wait-%e6%9a%b4%e6%b6%a8%e8%83%8c","status":"publish","type":"post","link":"https:\/\/www.wsisp.com\/helps\/98252.html","title":{"rendered":"\u522b\u518d\u602a ET \u6a21\u5f0f\u6f0f\u4e8b\u4ef6\u4e86\uff01\u6df1\u6316 C++ \u63a5\u5165\u7f51\u5173 CLOSE_WAIT \u66b4\u6da8\u80cc\u540e\u7684\u5185\u6838\u771f\u76f8\uff01"},"content":{"rendered":"<p>\u7f51\u5173\u76d1\u63a7\u544a\u8b66\u628a\u7fa4\u70b8\u4e86&#xff1a;ss -tan | grep -c CLOSE_WAIT\u00a0\u5728\u4e00\u53f0\u6838\u5fc3 C\u63a5\u5165\u7f51\u5173\u4e0a\u4ee5\u6bcf\u5929\u56db\u5343\u6761\u7684\u901f\u5ea6\u5355\u8c03\u98d9\u5347&#xff0c;\u76f4\u5230\u628a\u8fdb\u7a0b\u7684\u6587\u4ef6\u63cf\u8ff0\u7b26\u914d\u989d&#xff08;ulimit -n 65535&#xff09;\u5f7b\u5e95\u8017\u5c3d&#xff0c;accept4()\u00a0\u75af\u72c2\u629b\u51fa\u00a0EMFILE\u3002\u8be1\u5f02\u7684\u662f&#xff0c;\u4e0a\u6e38\u5fae\u670d\u52a1\u65e9\u5df2\u6355\u83b7\u5f02\u5e38\u8d85\u65f6\u5e76\u9500\u6bc1\u4e86\u8fde\u63a5&#xff0c;\u800c\u670d\u52a1\u7aef C\u00a0\u8fdb\u7a0b\u5185\u5b58\u91cc\u7684\u00a0std::shared_ptr&lt;TcpConnection&gt;\u00a0\u5374\u6b7b\u6b7b\u54ac\u4f4f\u4e0d\u653e&#xff0c;\u672c\u5730 Linux \u5185\u6838\u5c06\u5176\u6c38\u4e45\u9489\u6b7b\u5728\u00a0CLOSE_WAIT&#xff0c;\u5bf9\u7aef\u6293\u5305\u770b\u5374\u5168\u90fd\u662f\u00a0ESTABLISHED\u3002<\/p>\n<p>\u5f53\u65f6\u6211\u626b\u4e86\u4e00\u773c Reactor \u4e8b\u4ef6\u5faa\u73af&#xff0c;\u7b03\u5b9a\u662f\u8fb9\u7f18\u89e6\u53d1&#xff08;EPOLLET&#xff09;\u5199\u6f0f\u4e86\u4e8b\u4ef6&#xff0c;\u5f53\u5373\u628a\u00a0epoll\u00a0\u4ece ET \u5207\u56de\u6c34\u5e73\u89e6\u53d1&#xff08;LT&#xff09;&#xff0c;\u70ed\u91cd\u8f7d&#xff0c;\u76d1\u63a7\u4e0a\u7684 fd \u8ba1\u6570\u77ac\u95f4\u5f52\u96f6\u3002<\/p>\n<p>\u90a3\u6b21\u70ed\u4fee\u590d\u4e4b\u6240\u4ee5\u80fd\u300c\u6682\u65f6\u8d77\u6548\u300d&#xff0c;\u8ddf epoll \u7684\u89e6\u53d1\u6a21\u5f0f\u5173\u7cfb\u6781\u5c0f\u3002\u6211\u53ea\u662f\u7528 C\u5c42\u91cd\u65b0\u63a5\u6536\u6c34\u5e73\u901a\u77e5\u7684\u5f00\u9500\u6536\u7a84\u4e86\u6f0f\u8bfb\u7a97\u53e3&#xff0c;\u628a\u590d\u73b0\u5468\u671f\u4ece\u4e00\u5929\u62d6\u6210\u4e86\u4e09\u5929\u3002\u6211\u6389\u8fdb\u4e86\u4e00\u4e2a\u73b0\u4ee3 C\u00a0\u7f51\u7edc\u7f16\u7a0b\u6700\u5178\u578b\u7684\u8ba4\u77e5\u9677\u9631&#xff1a;\u628a C&#043;&#043; \u5bf9\u8c61\u7684\u751f\u547d\u5468\u671f&#xff0c;\u7b49\u540c\u4e8e\u7f51\u7edc\u8fde\u63a5\u7684\u771f\u5b9e\u751f\u547d\u5468\u671f\u3002<\/p>\n<p>\u6211\u4eec\u5728 C\u91cc\u5199 RAII \u5c01\u88c5\u00a0SocketFd\u3001\u7528\u00a0std::enable_shared_from_this\u00a0\u4f20\u9012\u95ed\u5305\u3001\u5728\u00a0EventLoop\u00a0\u91cc\u6ce8\u518c\u4e8b\u4ef6\u56de\u8c03&#xff0c;\u81ea\u4ee5\u4e3a\u638c\u63a7\u4e86\u8fde\u63a5\u3002\u4f46\u5728\u5e95\u5c42&#xff0c;\u8fd9\u6761\u6240\u8c13\u7684\u300cTCP \u8fde\u63a5\u300d\u672c\u8d28\u4e0a\u5728\u4e09\u5904\u72ec\u7acb\u7684\u5185\u5b58\u7a7a\u95f4\u91cc\u5404\u81ea\u5b58\u4e86\u4e00\u4efd\u5b8c\u5168\u89e3\u8026\u7684\u72b6\u6001\u526f\u672c&#xff1a;**\u4f60\u7684 C\u00a0\u7528\u6237\u6001\u8fdb\u7a0b\u3001\u672c\u7aef Linux \u534f\u8bae\u6808\u5185\u6838\u3001\u4ee5\u53ca\u5bf9\u7aef\u5185\u6838\u3002** \u5b83\u4eec\u53ea\u5728\u6781\u5ea6\u7a00\u758f\u7684\u7f51\u7edc\u6536\u53d1\u5305\u4e0e\u7cfb\u7edf\u8c03\u7528\u77ac\u95f4\u77ed\u6682\u5bf9\u9f50&#xff0c;\u5176\u4f59\u65f6\u95f4\u5168\u5728\u5404\u81ea\u6697\u4e2d\u6f02\u79fb\u3002<\/p>\n<p>IP \u5c42\u4ece\u6765\u4e0d\u5b58\u8fde\u63a5\u72b6\u6001&#xff0c;TCP \u53ea\u597d\u5728\u4e24\u7aef\u5185\u6838\u5404\u9020\u4e00\u4efd\u00a0struct tcp_sock&#xff0c;\u4f60\u7684 C\u8fdb\u7a0b\u624b\u91cc\u63e1\u7740\u7b2c\u4e09\u4efd\u5e94\u7528\u5c42\u72b6\u6001\u3002\u4e09\u4efd\u526f\u672c\u5404\u81ea\u6f02\u79fb&#xff0c;\u6240\u6709\u68d8\u624b\u7684\u751f\u4ea7\u7f51\u7edc\u6545\u969c&#xff0c;\u672c\u8d28\u4e0a\u90fd\u53ea\u95ee\u4e24\u4ef6\u4e8b&#xff1a;\u8fd9\u4e00\u523b\u54ea\u4e24\u4efd\u526f\u672c\u53d1\u751f\u4e86\u8ba4\u77e5\u6495\u88c2&#xff1f;\u8c01\u8be5\u5728\u4f55\u65f6\u8d1f\u8d23\u53d1\u73b0&#xff1f;\u00a0\u672c\u6587\u5c06\u4ece\u73b0\u4ee3 C\u00a0Reactor \u67b6\u6784\u4e0e\u5185\u6838\u6e90\u7801\u51fa\u53d1&#xff0c;\u62c6\u89e3\u00a0fs\/eventpoll.c\u00a0\u91cc\u533a\u5206 LT \u4e0e ET \u7684\u6838\u5fc3 7 \u884c\u903b\u8f91\u3001__tcp_close()\u00a0\u62ff RST \u9876\u66ff FIN \u7684\u5185\u6838\u5224\u636e\u3001\u672a\u8bfb\u5b8c\u7f13\u51b2\u533a\u5373\u6790\u6784\u5bfc\u81f4\u7684\u65ad\u8fde\u707e\u96be&#xff0c;\u4ee5\u53ca\u5185\u6838\u4e3a TIME_WAIT \u5199\u5165\u7684 pure paranoia\u3002<\/p>\n<h3>\u90a3\u6b21\u4fee\u590d\u6539\u5bf9\u4e86\u73b0\u8c61&#xff0c;\u6539\u9519\u4e86\u6839\u56e0<\/h3>\n<p>\u5148\u628a\u5f53\u65f6\u5728 C&#043;&#043; \u670d\u52a1\u7aef\u4e0e\u7ebf\u4e0a\u73af\u5883\u6293\u5230\u7684\u56db\u4e2a\u75c7\u72b6\u6446\u9f50&#xff0c;\u5b83\u4eec\u540e\u9762\u4f1a\u5404\u81ea\u7cbe\u786e\u5f52\u4f4d&#xff1a;<\/p>\n<ul>\n<li>\n<p>\u75c7\u72b6\u4e00&#xff08;C&#043;&#043; \u7528\u6237\u6001\u4e0e\u672c\u7aef\u5185\u6838\u6495\u88c2&#xff09;&#xff1a;ss -tan\u00a0\u91cc\u00a0CLOSE_WAIT\u00a0\u5355\u8c03\u589e\u957f\u6c38\u4e0d\u6d88\u9000&#xff0c;\u670d\u52a1\u8fdb\u7a0b\u5185\u6301\u6709\u7684\u00a0Connection\u00a0\u5b9e\u4f8b\u6570\u91cf\u4e0e\u5185\u6838 socket \u8ba1\u6570\u6b7b\u9501\u3002<\/p>\n<\/li>\n<li>\n<p>\u75c7\u72b6\u4e8c&#xff08;\u672c\u7aef\u5185\u6838\u4e0e\u5bf9\u7aef\u5185\u6838\u6495\u88c2&#xff09;&#xff1a;\u5ba2\u6237\u7aef\u4fa7\u65e9\u5df2\u00a0close()\u00a0\u5e76\u9000\u51fa&#xff0c;\u670d\u52a1\u7aef\u6293\u5305\u5374\u663e\u793a\u4ecd\u662f\u00a0ESTABLISHED&#xff0c;\u4e24\u7aef\u5185\u6838\u5bf9\u540c\u4e00\u7269\u7406\u94fe\u8def\u7684\u8ba4\u77e5\u622a\u7136\u76f8\u53cd\u3002<\/p>\n<\/li>\n<li>\n<p>\u75c7\u72b6\u4e09&#xff08;Reactor \u8c03\u5ea6\u5f00\u9500\u6fc0\u589e&#xff09;&#xff1a;\u5c06 epoll \u6539\u4e3a LT \u540e\u00a0CLOSE_WAIT\u00a0\u6682\u65f6\u5f52\u96f6&#xff0c;\u4f46 C&#043;&#043; \u4e8b\u4ef6\u5faa\u73af\u7ebf\u7a0b\u7684\u8f6f\u4e2d\u65ad&#xff08;si&#xff09;CPU \u5360\u7528\u77ac\u95f4\u66b4\u6da8 6~8 \u4e2a\u767e\u5206\u70b9\u3002<\/p>\n<\/li>\n<li>\n<p>\u75c7\u72b6\u56db&#xff08;\u5fc3\u8df3\u63a2\u6d4b\u673a\u5236\u6ede\u540e&#xff09;&#xff1a;\u540c\u4e8b\u4e3a\u5e95\u5c42 socket \u5f00\u542f\u00a0SO_KEEPALIVE\u00a0\u540e&#xff0c;\u6b21\u65e5\u6e05\u6668\u786e\u5b9e\u56de\u6536\u4e86\u4e00\u6279\u5b64\u513f\u8fde\u63a5&#xff0c;\u4f46\u6e05\u7406\u52a8\u4f5c\u5168\u90fd\u50f5\u6b7b\u5ef6\u8fdf\u5728 2 \u5c0f\u65f6\u4e4b\u540e\u3002<\/p>\n<\/li>\n<\/ul>\n<p>\u5f53\u65f6\u6211\u7ed9\u51fa\u7684\u6280\u672f\u590d\u76d8\u662f\u300cC&#043;&#043; \u5728 ET \u6a21\u5f0f\u4e0b\u7684\u00a0read()\u00a0\u5faa\u73af\u6ca1\u6709\u8bfb\u5230\u00a0EAGAIN&#xff0c;\u5c11\u5faa\u73af\u4e86\u4e00\u6b21\u5bfc\u81f4\u6f0f\u6389\u4e86 FIN \u5305\u300d\u3002\u8fd9\u4e2a\u89e3\u91ca\u770b\u4f3c\u5207\u4e2d\u8981\u5bb3&#xff0c;\u80fd\u89e3\u91ca\u75c7\u72b6\u4e00\u548c\u75c7\u72b6\u4e09&#xff0c;\u5374\u5bf9\u75c7\u72b6\u4e8c\u548c\u75c7\u72b6\u56db\u5b8c\u5168\u65e0\u80fd\u4e3a\u529b\u3002\u4e00\u4e2a\u53ea\u80fd\u89e3\u91ca\u4e00\u534a\u73b0\u8c61\u7684\u7406\u8bba\u6a21\u578b&#xff0c;\u5728\u751f\u4ea7\u73af\u5883\u5fc5\u7136\u4f1a\u4ee5\u65b0\u7684\u5f62\u6001\u590d\u53d1\u3002<\/p>\n<p>\u771f\u6b63\u628a\u6211\u62fd\u56de\u6b63\u8f68\u7684&#xff0c;\u662f Linux \u6e90\u7801\u00a0net\/ipv4\/tcp_minisocks.c\u00a0\u91cc\u5173\u4e8e\u00a0tcp_timewait_state_process()\u00a0\u7684\u4e00\u6bb5\u6ce8\u91ca\u3002\u5185\u6838\u5f00\u53d1\u8005\u5199\u9053&#xff1a;TIME_WAIT \u5b58\u5728\u7684\u4e3b\u8981\u76ee\u7684&#xff0c;\u662f\u5f53\u5bf9\u7aef\u5361\u5728\u00a0LAST_ACK\u00a0\u53cd\u590d\u91cd\u4f20 FIN\u3001\u800c\u6211\u65b9\u56de\u9001\u7684 ACK \u53c8\u5728\u9014\u4e22\u5931\u65f6&#xff0c;\u4fdd\u8bc1\u8fde\u63a5\u4f9d\u7136\u80fd\u88ab\u4f18\u96c5\u95ed\u5408\u2014\u2014\u90a3\u53e5\u539f\u8bdd\u00a0one or more of our ACKs are lost&#xff0c;\u8bb2\u7684\u5b8c\u5168\u662f\u6211\u65b9\u53d1\u51fa\u7684 ACK \u62a5\u6587\u3002<\/p>\n<p>\u8fd9\u6bb5\u6ce8\u91ca\u70b9\u9192\u4e86\u6211&#xff1a;\u672c\u7aef C&#043;&#043; \u4e1a\u52a1\u54ea\u6015\u65e9\u5df2\u5b8c\u6210\u8ba1\u7b97\u5e76\u9500\u6bc1\u4e86\u6240\u6709\u8d44\u6e90&#xff0c;Linux \u5185\u6838\u4ecd\u8981\u5728\u5185\u5b58\u4e2d\u6b7b\u5b88 60 \u79d2&#xff0c;\u4ec5\u4ec5\u662f\u4e3a\u4e86\u7ed9\u5bf9\u7aef\u90a3\u4efd\u53ef\u80fd\u5931\u6b65\u7684\u72b6\u6001\u526f\u672c\u515c\u5e95\u3002<\/p>\n<p>\u4ece\u8fd9\u4e00\u523b\u8d77&#xff0c;\u6574\u5957\u7f51\u7edc\u67b6\u6784\u7684\u8ba4\u77e5\u88ab\u5f7b\u5e95\u91cd\u6784\u3002\u6211\u4eec\u5e73\u65f6\u5728 C\u91cc\u901a\u8fc7\u00a0std::unique_ptr\u00a0\u6216\u667a\u80fd\u6307\u9488\u7ba1\u7406\u7684\u4e0d\u662f\u4ec0\u4e48\u300c\u7f51\u7edc\u7ba1\u9053\u300d&#xff0c;\u800c\u4ec5\u4ec5\u662f\u7b2c\u4e09\u4efd\u5e94\u7528\u5c42\u526f\u672c\u3002\u5185\u6838\u773c\u91cc\u6839\u672c\u6ca1\u6709\u8fde\u63a5&#xff0c;\u53ea\u6709\u4e00\u5806\u7531\u5b9a\u65f6\u5668\u9a71\u52a8\u7684\u672c\u5730\u7ed3\u6784\u4f53&#xff0c;\u4ee5\u53ca\u4e00\u5957\u7528\u6765\u63a8\u6d4b\u5bf9\u7aef\u72b6\u6001\u7684\u6982\u7387\u6027\u89c4\u5219\u3002CLOSE_WAIT\u00a0\u662f C\u00a0\u4ee3\u7801\u672a\u54cd\u5e94\u5185\u6838\u5173\u95ed\u4e8b\u4ef6\u7684\u7ed3\u679c&#xff0c;TIME_WAIT\u00a0\u662f\u5185\u6838\u4e3a\u5bf9\u7aef\u5931\u6b65\u4e70\u7684\u5355&#xff0c;\u800c ET \u4e0e LT&#xff0c;\u4e0d\u8fc7\u662f\u51b3\u5b9a\u4f60\u7684 C&#043;&#043; \u4e8b\u4ef6\u5faa\u73af\u4f55\u65f6\u3001\u4ee5\u4f55\u79cd\u4ee3\u4ef7\u53bb\u540c\u6b65\u8fd9\u4e09\u4efd\u526f\u672c\u3002<\/p>\n<p>\u6211\u90a3\u6b21\u70ed\u4fee&#xff0c;\u4ec5\u4ec5\u662f\u5728 C&#043;&#043; \u5c42\u7ed9\u7b2c\u4e09\u4efd\u526f\u672c\u6253\u4e86\u5757\u6b62\u75db\u8d34\u3002<\/p>\n<h3>\u4e00\u6761\u8fde\u63a5\u540c\u65f6\u6d3b\u5728\u4e09\u5904\u5185\u5b58\u91cc<\/h3>\n<p>\u628a TCP \u7684\u590d\u6742\u5ea6\u5f52\u5230\u4e00\u53e5\u8bdd&#xff1a;IP \u662f\u65e0\u72b6\u6001\u7684&#xff0c;\u800c\u5e94\u7528\u8981\u7684\u662f\u6709\u72b6\u6001\u7684\u5b57\u8282\u6d41&#xff0c;\u4e8e\u662f\u72b6\u6001\u53ea\u80fd\u7531\u4e24\u7aef\u5404\u81ea\u4fdd\u5b58\u4e00\u4efd&#xff0c;\u9760\u62a5\u6587\u6765\u56de\u540c\u6b65\u3002RFC 9293 \u5728 \u00a73.5.1 \u5b9a\u4e49\u534a\u5f00\u8fde\u63a5\u65f6\u628a\u8fd9\u5c42\u610f\u601d\u5199\u5f97\u5f88\u76f4\u767d&#xff1a;<\/p>\n<p>text<\/p>\n<p>An established connection is said to be &#034;half-open&#034; if<br \/>\none of the TCP peers has closed or aborted the<br \/>\nconnection at its end without the knowledge of the<br \/>\nother.<\/p>\n<p>without the knowledge of the other\u00a0\u662f\u6574\u4efd\u6587\u6863\u91cc\u6700\u5173\u952e\u7684\u516d\u4e2a\u8bcd\u3002\u6807\u51c6\u672c\u8eab\u5c31\u627f\u8ba4&#xff0c;\u4e24\u7aef\u5bf9\u540c\u4e00\u6761\u8fde\u63a5\u7684\u8ba4\u77e5\u53ef\u4ee5\u4e0d\u4e00\u81f4&#xff0c;\u800c\u4e14\u5b83\u628a\u8fd9\u79cd\u4e0d\u4e00\u81f4\u547d\u540d\u6210\u4e86\u4e00\u4e2a\u6b63\u5f0f\u72b6\u6001\u3002<\/p>\n<p>\u7b2c\u4e09\u4efd\u526f\u672c\u6807\u51c6\u91cc\u6ca1\u5199&#xff0c;\u56e0\u4e3a\u5b83\u5728\u6807\u51c6\u7684\u7ba1\u8f96\u8303\u56f4\u4e4b\u5916&#xff0c;\u4f46\u5b83\u5bf9\u5199\u670d\u52a1\u7aef\u7684\u4eba\u6700\u91cd\u8981\u3002\u4f60\u7684\u8fdb\u7a0b\u624b\u91cc\u63e1\u7740\u7684\u4e1c\u897f\u662f&#xff1a;\u4e00\u4e2a fd\u3001\u4e00\u4efd\u300c\u4e0a\u6b21 epoll \u544a\u8bc9\u6211\u7684\u4e8b\u4ef6\u300d\u3001\u4e00\u4efd\u300c\u6211\u4ee5\u4e3a\u5bf9\u7aef\u8fd8\u5728\u300d\u7684\u4e1a\u52a1\u5047\u8bbe\u3002\u8fd9\u4e09\u6837\u52a0\u8d77\u6765\u5c31\u662f\u5e94\u7528\u5c42\u5bf9\u8fd9\u6761\u8fde\u63a5\u7684\u8ba4\u77e5&#xff0c;\u5b83\u8ddf\u5185\u6838\u90a3\u4efd\u9760\u7cfb\u7edf\u8c03\u7528\u540c\u6b65&#xff0c;\u800c\u7cfb\u7edf\u8c03\u7528\u662f\u7a00\u758f\u7684\u3001\u7531\u4f60\u81ea\u5df1\u51b3\u5b9a\u4ec0\u4e48\u65f6\u5019\u53d1\u8d77\u7684\u3002<\/p>\n<p>text<\/p>\n<p> \u8fdb\u7a0b\u526f\u672c            \u672c\u7aef\u5185\u6838\u526f\u672c          \u5bf9\u7aef\u5185\u6838\u526f\u672c<br \/>\n \u250c\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2510      \u250c\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2510      \u250c\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2510<br \/>\n \u2502 fd 4     \u2502      \u2502 tcp_sock   \u2502      \u2502 tcp_sock   \u2502<br \/>\n \u2502 \u4e8b\u4ef6\u7f13\u5b58  \u2502\u25c4\u2500\u2500\u2500\u2500\u25ba\u2502 state      \u2502\u25c4\u2500\u2500\u2500\u2500\u25ba\u2502 state      \u2502<br \/>\n \u2502 \u4e1a\u52a1\u5047\u8bbe  \u2502 \u7cfb\u7edf  \u2502 seq \/ ack  \u2502 \u62a5\u6587  \u2502 seq \/ ack  \u2502<br \/>\n \u2514\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2518 \u8c03\u7528  \u2514\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2518      \u2514\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2518<br \/>\n      \u25b2                   \u25b2                   \u25b2<br \/>\n   \u4f60\u51b3\u5b9a\u4f55\u65f6\u540c\u6b65      \u5185\u6838\u51b3\u5b9a\u4f55\u65f6\u540c\u6b65     \u5bf9\u7aef\u51b3\u5b9a<\/p>\n<p>\u4e09\u6761\u540c\u6b65\u94fe\u8def\u7684\u6027\u8d28\u5b8c\u5168\u4e0d\u540c&#xff0c;\u8fd9\u662f\u540e\u9762\u6240\u6709\u9898\u76ee\u7684\u5206\u6c34\u5cad\u3002<\/p>\n<p>\u8fdb\u7a0b\u4e0e\u672c\u7aef\u5185\u6838\u4e4b\u95f4&#xff1a;\u540c\u6b65\u662f\u4f60\u4e3b\u52a8\u53d1\u8d77\u7684&#xff0c;\u9760\u00a0read\u00a0\/\u00a0write\u00a0\/\u00a0epoll_wait\u00a0\/\u00a0getsockopt\u3002\u5185\u6838\u53ef\u4ee5\u63a8\u4e00\u4e2a\u901a\u77e5\u7ed9\u4f60&#xff0c;\u4f46\u63a8\u5b8c\u5c31\u7b97\u5b8c\u6210\u4e86\u4e49\u52a1&#xff0c;\u5b83\u5e76\u4e0d\u68c0\u67e5\u4f60\u6709\u6ca1\u6709\u771f\u7684\u53bb\u8bfb\u3002<\/p>\n<p>\u672c\u7aef\u5185\u6838\u4e0e\u5bf9\u7aef\u5185\u6838\u4e4b\u95f4&#xff1a;\u540c\u6b65\u662f\u62a5\u6587\u9a71\u52a8\u7684&#xff0c;\u53ea\u6709\u771f\u7684\u53d1\u51fa\u53bb\u4e00\u4e2a\u5305\u5e76\u6536\u5230\u56de\u5e94&#xff0c;\u4e24\u4efd\u526f\u672c\u624d\u5bf9\u5f97\u4e0a\u3002\u94fe\u8def\u7a7a\u95f2\u65f6&#xff0c;\u4e24\u7aef\u53ef\u4ee5\u4efb\u610f\u6f02\u79fb&#xff0c;\u8c01\u4e5f\u53d1\u73b0\u4e0d\u4e86\u8c01\u3002<\/p>\n<p>\u8fdb\u7a0b\u4e0e\u5bf9\u7aef\u5185\u6838\u4e4b\u95f4&#xff1a;\u6ca1\u6709\u76f4\u63a5\u94fe\u8def\u3002\u4f60\u5bf9\u5bf9\u7aef\u7684\u6240\u6709\u8ba4\u77e5&#xff0c;\u90fd\u662f\u672c\u7aef\u5185\u6838\u8f6c\u8ff0\u7ed9\u4f60\u7684\u4e8c\u624b\u4fe1\u606f&#xff0c;\u800c\u672c\u7aef\u5185\u6838\u7684\u4fe1\u606f\u672c\u8eab\u4e5f\u53ef\u80fd\u8fc7\u671f\u3002<\/p>\n<p>\u8fd9\u4e2a\u6a21\u578b\u6709\u4e24\u5904\u5fc5\u987b\u5148\u8bf4\u6e05\u7684\u5931\u6548\u70b9&#xff0c;\u5426\u5219\u5b83\u4f1a\u628a\u4eba\u5e26\u5230\u9519\u7684\u65b9\u5411\u53bb\u3002<\/p>\n<p>\u5b83\u6570\u51fa\u6765\u7684\u4e09\u4efd&#xff0c;\u53ea\u5728\u4e24\u7aef\u76f4\u8fde\u65f6\u624d\u662f\u4e09\u4efd\u3002\u00a0\u73b0\u5b9e\u94fe\u8def\u4e0a\u6bcf\u4e00\u4e2a\u6709\u72b6\u6001\u7684\u4e2d\u95f4\u8bbe\u5907\u2014\u2014NAT\u3001\u56db\u5c42\u8d1f\u8f7d\u5747\u8861\u3001\u5e26\u4f1a\u8bdd\u8868\u7684\u9632\u706b\u5899\u2014\u2014\u90fd\u5404\u81ea\u6301\u6709\u4e00\u4efd&#xff0c;\u800c\u5b83\u4eec\u7684\u8001\u5316\u89c4\u5219\u8ddf\u4e24\u7aef\u5185\u6838\u65e0\u5173&#xff0c;\u4e5f\u4e0d\u53d7\u4efb\u4f55\u4e00\u7aef\u63a7\u5236\u3002\u957f\u8fde\u63a5\u4e0a\u90a3\u79cd\u300c\u4e24\u7aef\u90fd\u8bf4\u81ea\u5df1\u4e00\u5207\u6b63\u5e38\u3001\u5305\u5c31\u662f\u4e0d\u901a\u300d\u7684\u6545\u969c&#xff0c;\u6210\u56e0\u901a\u5e38\u5c31\u5728\u8fd9\u4e9b\u526f\u672c\u91cc\u3002\u51c6\u786e\u7684\u8bf4\u6cd5\u662f\u300c\u4e09\u4efd&#xff0c;\u52a0\u4e0a\u8def\u5f84\u4e0a\u6bcf\u4e00\u8df3\u6709\u72b6\u6001\u8bbe\u5907\u5404\u4e00\u4efd\u300d&#xff1b;\u6211\u7528\u4e09\u4efd&#xff0c;\u662f\u56e0\u4e3a\u524d\u4e09\u4efd\u80fd\u89e3\u91ca\u7edd\u5927\u591a\u6570\u843d\u5728\u4ee3\u7801\u5c42\u9762\u7684\u73b0\u8c61&#xff0c;\u4e00\u65e6\u6545\u969c\u7684\u5f62\u72b6\u53d8\u6210\u300c\u4e24\u7aef\u90fd\u6b63\u5e38\u300d&#xff0c;\u5c31\u5f97\u5f80\u8def\u5f84\u4e0a\u627e\u7b2c\u56db\u4efd\u3002<\/p>\n<p>\u5b83\u5bf9\u7eaf\u541e\u5410\u4e0e\u5ef6\u8fdf\u7c7b\u95ee\u9898\u5b8c\u5168\u65e0\u80fd\u4e3a\u529b\u3002\u00a0Nagle \u4e0e\u5ef6\u8fdf\u786e\u8ba4\u4e92\u76f8\u7b49\u5f85\u9020\u6210\u7684\u90a3\u79cd\u56db\u5341\u6beb\u79d2\u6bdb\u523a\u3001\u7f13\u51b2\u533a\u81a8\u80c0\u3001\u591a\u6253\u4e00\u7684 incast\u2014\u2014\u8fd9\u4e9b\u573a\u666f\u91cc\u4e09\u4efd\u526f\u672c\u81ea\u59cb\u81f3\u7ec8\u4fdd\u6301\u4e00\u81f4&#xff0c;\u6162\u662f\u6392\u961f\u9020\u6210\u7684&#xff0c;\u8ddf\u8c01\u77e5\u4e0d\u77e5\u9053\u8c01\u6beb\u65e0\u5173\u7cfb\u3002\u62ff\u4e00\u4e2a\u8bb2\u4e00\u81f4\u6027\u7684\u6a21\u578b\u53bb\u89e3\u91ca\u6027\u80fd\u73b0\u8c61&#xff0c;\u662f\u5b83\u6700\u5bb9\u6613\u88ab\u8bef\u7528\u7684\u65b9\u5f0f&#xff0c;\u800c\u4e14\u8bef\u7528\u4e4b\u540e\u4f1a\u4e00\u76f4\u5728\u9519\u7684\u5730\u65b9\u627e\u8bc1\u636e\u3002<\/p>\n<p>\u6211\u628a\u8fd9\u5957\u4e1c\u897f\u53eb\u505a\u4e09\u526f\u672c\u6a21\u578b&#xff0c;\u63a5\u4e0b\u6765\u7684\u6bcf\u4e00\u8282\u90fd\u662f\u5728\u95ee\u540c\u4e00\u7ec4\u95ee\u9898&#xff1a;\u8fd9\u4e00\u523b\u54ea\u4e24\u4efd\u526f\u672c\u5206\u6b67\u4e86&#xff0c;\u5206\u6b67\u7531\u8c01\u53d1\u73b0&#xff0c;\u53d1\u73b0\u8981\u591a\u4e45\u3002\u4e5d\u9053\u5e38\u89c1\u9898\u5728\u8fd9\u4e2a\u5750\u6807\u7cfb\u91cc\u5404\u5360\u4e00\u683c\u3002<\/p>\n<table>\n<tbody>\n<tr>\n<p>\u9898\u76ee<\/p>\n<p>\u5206\u6b67\u53d1\u751f\u5728\u54ea\u4e24\u4efd\u4e4b\u95f4<\/p>\n<\/tr>\n<tr>\n<td>\n<p>\u6c34\u5e73\u89e6\u53d1\u4e0e\u8fb9\u7f18\u89e6\u53d1<\/p>\n<\/td>\n<td>\n<p>\u8fdb\u7a0b \u2194 \u672c\u7aef\u5185\u6838<\/p>\n<\/td>\n<\/tr>\n<tr>\n<td>\n<p>CLOSE_WAIT<\/p>\n<\/td>\n<td>\n<p>\u8fdb\u7a0b \u2194 \u672c\u7aef\u5185\u6838<\/p>\n<\/td>\n<\/tr>\n<tr>\n<td>\n<p>\u534a\u5173\u95ed<\/p>\n<\/td>\n<td>\n<p>\u8fdb\u7a0b \u2194 \u672c\u7aef\u5185\u6838&#xff08;\u65b9\u5411\u7c92\u5ea6&#xff09;<\/p>\n<\/td>\n<\/tr>\n<tr>\n<td>\n<p>TIME_WAIT<\/p>\n<\/td>\n<td>\n<p>\u672c\u7aef\u5185\u6838\u4e3a\u5bf9\u7aef\u526f\u672c\u515c\u5e95<\/p>\n<\/td>\n<\/tr>\n<tr>\n<td>\n<p>\u4e09\u6b21\u63e1\u624b\u4e0e\u56db\u6b21\u6325\u624b<\/p>\n<\/td>\n<td>\n<p>\u5efa\u7acb\u4e0e\u62c6\u9664\u4e24\u7aef\u526f\u672c<\/p>\n<\/td>\n<\/tr>\n<tr>\n<td>\n<p>\u534a\u5f00\u8fde\u63a5<\/p>\n<\/td>\n<td>\n<p>\u672c\u7aef\u5185\u6838 \u2194 \u5bf9\u7aef\u5185\u6838<\/p>\n<\/td>\n<\/tr>\n<tr>\n<td>\n<p>\u53ef\u9760\u6027\u673a\u5236<\/p>\n<\/td>\n<td>\n<p>\u672c\u7aef\u5185\u6838 \u2194 \u5bf9\u7aef\u5185\u6838<\/p>\n<\/td>\n<\/tr>\n<tr>\n<td>\n<p>MTU \u4e0e MSS<\/p>\n<\/td>\n<td>\n<p>\u4e24\u7aef\u526f\u672c\u5bf9\u8def\u5f84\u7684\u5047\u8bbe<\/p>\n<\/td>\n<\/tr>\n<tr>\n<td>\n<p>\u6536\u53d1\u5305\u8def\u5f84<\/p>\n<\/td>\n<td>\n<p>\u526f\u672c\u7684\u7269\u7406\u8f7d\u4f53<\/p>\n<\/td>\n<\/tr>\n<tr>\n<td>\n<p>UDP<\/p>\n<\/td>\n<td>\n<p>\u653e\u5f03\u524d\u4e24\u4efd&#xff0c;\u53ea\u7559\u4f60\u81ea\u5df1\u90a3\u4efd<\/p>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<h3>\u8fb9\u7f18\u89e6\u53d1\u5728\u5185\u6838\u91cc\u53ea\u662f\u5c11\u4e86\u4e00\u4e2a else if<\/h3>\n<p>\u5148\u95ee\u4e00\u4e2a\u5177\u4f53\u95ee\u9898&#xff1a;ET \u6a21\u5f0f\u51ed\u4ec0\u4e48\u80fd\u7701\u6389\u91cd\u590d\u901a\u77e5\u3002\u591a\u6570\u8bb2\u89e3\u4f1a\u8bf4\u5b83\u300c\u53ea\u5728\u72b6\u6001\u53d8\u5316\u7684\u8fb9\u6cbf\u901a\u77e5\u4e00\u6b21\u300d&#xff0c;\u8fd9\u53e5\u8bdd\u63cf\u8ff0\u4e86\u884c\u4e3a&#xff0c;\u6ca1\u6709\u89e3\u91ca\u673a\u5236&#xff0c;\u800c\u673a\u5236\u5728\u00a0fs\/eventpoll.c\u00a0\u91cc&#xff0c;\u4e00\u5171\u4e03\u884c\u3002<\/p>\n<p>epoll \u7684\u5c31\u7eea\u961f\u5217\u53eb\u00a0ep-&gt;rdllist\u3002\u7f51\u5361\u6536\u5230\u6570\u636e\u3001\u534f\u8bae\u6808\u628a skb \u6302\u8fdb socket \u63a5\u6536\u961f\u5217\u4e4b\u540e&#xff0c;\u4f1a\u8c03\u7528\u00a0sk_data_ready&#xff0c;\u6700\u7ec8\u8d70\u5230 epoll \u6ce8\u518c\u7684\u56de\u8c03\u00a0ep_poll_callback()&#xff0c;\u90a3\u91cc\u5e72\u7684\u4e8b\u5c31\u4e00\u4ef6&#xff1a;<\/p>\n<p>C<\/p>\n<p>\/* fs\/eventpoll.c, Linux 6.6, ep_poll_callback() *\/<br \/>\n} else if (!ep_is_linked(epi)) {<br \/>\n    \/* In the usual case, add event to ready list. *\/<br \/>\n    if (list_add_tail_lockless(&amp;epi-&gt;rdllink, &amp;ep-&gt;rdllist))<br \/>\n        ep_pm_stay_awake_rcu(epi);<br \/>\n}<\/p>\n<p>\u6ce8\u610f\u00a0!ep_is_linked(epi)\u00a0\u8fd9\u4e2a\u5224\u65ad&#xff1a;\u5df2\u7ecf\u5728\u5c31\u7eea\u961f\u5217\u91cc\u7684 epitem \u4e0d\u4f1a\u88ab\u91cd\u590d\u6302\u3002\u6240\u4ee5\u300c\u6570\u636e\u5230\u8fbe\u300d\u8fd9\u4e2a\u4e8b\u4ef6&#xff0c;\u5728\u5185\u6838\u4fa7\u672c\u6765\u5c31\u53ea\u4f1a\u5165\u961f\u4e00\u6b21&#xff0c;\u8ddf\u4f60\u7528 LT \u8fd8\u662f ET \u65e0\u5173\u3002<\/p>\n<p>\u5dee\u522b\u51fa\u73b0\u5728\u51fa\u961f\u7684\u90a3\u4e00\u4fa7\u3002ep_send_events()\u00a0\u628a\u5c31\u7eea\u4e8b\u4ef6\u62f7\u7ed9\u7528\u6237\u6001\u4e4b\u540e&#xff0c;\u8981\u51b3\u5b9a\u8fd9\u4e2a epitem \u662f\u7559\u4e0b\u8fd8\u662f\u4e22\u6389&#xff1a;<\/p>\n<p>C<\/p>\n<p>\/* fs\/eventpoll.c, Linux 6.6, ep_send_events() *\/<br \/>\nif (epi-&gt;event.events &amp; EPOLLONESHOT)<br \/>\n    epi-&gt;event.events &amp;&#061; EP_PRIVATE_BITS;<br \/>\nelse if (!(epi-&gt;event.events &amp; EPOLLET)) {<br \/>\n    \/*<br \/>\n     * If this file has been added with Level<br \/>\n     * Trigger mode, we need to insert back inside<br \/>\n     * the ready list, so that the next call to<br \/>\n     * epoll_wait() will check again the events<br \/>\n     * availability.<br \/>\n     *\/<br \/>\n    list_add_tail(&amp;epi-&gt;rdllink, &amp;ep-&gt;rdllist);<br \/>\n    ep_pm_stay_awake(epi);<br \/>\n}<\/p>\n<p>\u5c31\u8fd9\u4e9b\u3002LT \u662f\u4e00\u4e2a\u989d\u5916\u52a8\u4f5c&#xff1a;\u628a\u521a\u521a\u62a5\u544a\u8fc7\u7684 epitem \u91cd\u65b0\u585e\u56de\u5c31\u7eea\u961f\u5217&#xff0c;\u8ba9\u4e0b\u4e00\u6b21\u00a0epoll_wait()\u00a0\u518d\u67e5\u4e00\u904d\u5f53\u524d\u72b6\u6001\u3002ET \u662f\u8fd9\u4e2a\u52a8\u4f5c\u7684\u7f3a\u5e2d\u3002\u00a0\u5185\u6838\u91cc\u6839\u672c\u6ca1\u6709\u4e00\u6bb5\u4ee3\u7801\u4e13\u95e8\u8d1f\u8d23\u300c\u68c0\u6d4b\u8fb9\u6cbf\u300d&#xff0c;\u6240\u8c13\u8fb9\u6cbf&#xff0c;\u662f\u91cd\u65b0\u5165\u961f\u8fd9\u4e2a\u52a8\u4f5c\u88ab\u8df3\u8fc7\u4e4b\u540e\u7684\u89c2\u611f\u3002<\/p>\n<p>\u628a\u5b83\u7ffb\u8bd1\u6210\u526f\u672c\u8bed\u8a00&#xff0c;\u4e24\u79cd\u6a21\u5f0f\u7684\u8bed\u4e49\u5c31\u7cbe\u786e\u4e86\u3002<\/p>\n<p>LT \u662f\u72b6\u6001\u540c\u6b65&#xff1a;\u6bcf\u6b21\u00a0epoll_wait()\u00a0\u8fd4\u56de\u65f6&#xff0c;\u5185\u6838\u628a\u300c\u6b64\u523b\u63a5\u6536\u961f\u5217\u975e\u7a7a\u300d\u8fd9\u4e2a\u5f53\u524d\u72b6\u6001\u91cd\u65b0\u544a\u8bc9\u4f60\u4e00\u904d\u3002\u4f60\u6f0f\u8bfb\u4e86\u4e5f\u6ca1\u5173\u7cfb&#xff0c;\u4e0b\u4e00\u8f6e\u5b83\u8fd8\u5728\u3002\u4ee3\u4ef7\u662f\u6bcf\u4e00\u8f6e\u90fd\u8981\u4e3a\u6bcf\u4e2a\u5c31\u7eea fd \u91cd\u65b0\u8c03\u4e00\u6b21\u00a0ep_item_poll()\u00a0\u53bb\u67e5\u72b6\u6001&#xff0c;\u5c31\u7eea fd \u591a\u7684\u65f6\u5019\u8fd9\u662f\u5b9e\u6253\u5b9e\u7684\u5f00\u9500\u2014\u2014\u6211\u90a3\u6b21\u6539\u56de LT \u4e4b\u540e\u6bcf\u6838 si \u6da8\u7684\u516d\u5230\u516b\u4e2a\u767e\u5206\u70b9&#xff0c;\u51fa\u5904\u5c31\u5728\u8fd9\u91cc&#xff0c;\u75c7\u72b6\u4e09\u5f52\u4f4d\u3002<\/p>\n<p>ET \u662f\u589e\u91cf\u540c\u6b65&#xff1a;\u5185\u6838\u53ea\u5728\u00a0ep_poll_callback()\u00a0\u88ab\u89e6\u53d1\u7684\u90a3\u4e00\u523b\u63a8\u7ed9\u4f60\u4e00\u6b21\u5dee\u5206\u3002\u5dee\u5206\u63a8\u5b8c&#xff0c;\u5185\u6838\u8ba4\u4e3a\u4f60\u5df2\u77e5\u6653&#xff0c;\u5b83\u7684\u8bb0\u8d26\u91cc\u8fd9\u6761 fd \u5c31\u662f\u5e72\u51c0\u7684\u3002\u4f60\u5982\u679c\u6ca1\u628a\u5dee\u5206\u5e94\u7528\u5b8c\u6574&#xff0c;\u5185\u6838\u4e0d\u4f1a\u91cd\u53d1&#xff0c;\u56e0\u4e3a\u5728\u5b83\u770b\u6765\u91cd\u53d1\u5df2\u7ecf\u53d1\u751f\u8fc7\u4e86\u3002<\/p>\n<p>\u8fd9\u4e2a\u5dee\u522b\u6709\u4e00\u4e2a\u5f88\u53cd\u76f4\u89c9\u7684\u63a8\u8bba&#xff1a;ET \u5e76\u4e0d\u6bd4 LT\u300c\u66f4\u5feb\u901a\u77e5\u300d&#xff0c;\u4e24\u8005\u7684\u901a\u77e5\u65f6\u673a\u5b8c\u5168\u4e00\u6837&#xff0c;\u90fd\u5728\u00a0ep_poll_callback()\u00a0\u90a3\u4e00\u523b\u3002ET \u7701\u4e0b\u7684\u662f LT \u6bcf\u8f6e\u91cd\u67e5\u72b6\u6001\u7684\u90a3\u90e8\u5206\u5f00\u9500&#xff0c;\u4ee3\u4ef7\u662f\u628a\u300c\u8bfb\u5e72\u51c0\u300d\u7684\u8d23\u4efb\u4ece\u5185\u6838\u8f6c\u79fb\u7ed9\u4e86\u4f60\u3002\u5c31\u7eea fd \u6570\u91cf\u5c11\u7684\u65f6\u5019&#xff0c;\u8fd9\u7b14\u8f6c\u79fb\u6362\u4e0d\u6765\u4ec0\u4e48&#xff1b;\u6bcf\u8f6e\u5c31\u7eea\u51e0\u4e07\u4e2a fd \u7684\u63a5\u5165\u5c42&#xff0c;\u5b83\u503c\u3002<\/p>\n<p>\u987a\u5e26\u8bf4\u6e05\u4e00\u4e2a\u5e38\u89c1\u8bef\u89e3&#xff1a;EPOLLET\u00a0\u4e0d\u6539\u53d8\u53ef\u8bfb\u7684\u5224\u5b9a\u6761\u4ef6&#xff0c;\u5b83\u53ea\u6539\u53d8 epitem \u7684\u53bb\u7559\u3002\u6709\u4eba\u4ee5\u4e3a ET \u4e0b\u300c\u7f13\u51b2\u533a\u4ece\u7a7a\u53d8\u975e\u7a7a\u624d\u901a\u77e5\u300d&#xff0c;\u5176\u5b9e\u662f\u300c\u975e\u7a7a\u671f\u95f4\u7684\u7b2c\u4e8c\u6b21\u4ee5\u540e\u4e0d\u518d\u5165\u961f\u300d&#xff0c;\u56e0\u4e3a\u00a0ep_is_linked\u00a0\u5df2\u7ecf\u62e6\u4f4f\u4e86\u3002\u7f13\u51b2\u533a\u91cc\u8fd8\u5269\u6570\u636e\u3001\u4f60\u53c8\u8bfb\u8d70\u4e00\u90e8\u5206\u4e4b\u540e\u65b0\u6570\u636e\u5230\u8fbe&#xff0c;ep_poll_callback\u00a0\u7167\u6837\u89e6\u53d1&#xff0c;\u7167\u6837\u901a\u77e5\u2014\u2014\u53ea\u8981\u90a3\u65f6 epitem \u5df2\u7ecf\u51fa\u961f\u4e86\u3002<\/p>\n<h3>\u628a ET \u5199\u9519\u7684\u90a3\u4e2a\u5faa\u73af\u957f\u4ec0\u4e48\u6837<\/h3>\n<p>\u4e0a\u4e00\u8282\u7684\u7ed3\u8bba\u843d\u5230\u4ee3\u7801\u4e0a\u5c31\u4e00\u53e5&#xff1a;ET \u4e0b\u6bcf\u6b21\u62ff\u5230\u4e8b\u4ef6&#xff0c;\u5fc5\u987b\u4e00\u76f4\u8bfb\u5230\u5185\u6838\u660e\u786e\u544a\u8bc9\u4f60\u300c\u6ca1\u6709\u4e86\u300d\u3002\u800c\u5185\u6838\u8868\u8fbe\u300c\u6ca1\u6709\u4e86\u300d\u7684\u65b9\u5f0f\u53ea\u6709\u4e00\u4e2a&#xff0c;read\u00a0\u8fd4\u56de -1 \u4e14\u00a0errno &#061;&#061; EAGAIN\u3002<\/p>\n<p>\u5199\u9519\u7684\u7248\u672c\u957f\u8fd9\u6837&#xff0c;\u5b83\u5728\u538b\u6d4b\u91cc\u80fd\u8dd1&#xff0c;\u5728\u751f\u4ea7\u91cc\u4f1a\u6f0f&#xff1a;<\/p>\n<p>C&#043;&#043;<\/p>\n<p>\/\/ \u4f1a\u6f0f\u4e8b\u4ef6\u7684 ET \u8bfb\u5faa\u73af<br \/>\nif (ev.events &amp; EPOLLIN) {<br \/>\n    char buf[65536];<br \/>\n    ssize_t n &#061; ::read(fd, buf, sizeof buf);   \/\/ \u53ea\u8bfb\u4e00\u6b21<br \/>\n    if (n &gt; 0) on_data(buf, n);<br \/>\n    else if (n &#061;&#061; 0) on_peer_closed(fd);<br \/>\n}<\/p>\n<p>read\u00a0\u662f\u6709\u4e0a\u754c\u7684\u3002\u5bf9\u7aef\u4e00\u6b21\u00a0write\u00a0\u4e86 100 KB&#xff0c;\u5185\u6838\u63a5\u6536\u961f\u5217\u91cc\u8eba\u7740 100 KB&#xff0c;\u8fd9\u6bb5\u4ee3\u7801\u8bfb\u8d70 64 KB \u5c31\u8fd4\u56de\u4e86\u3002\u5269\u4e0b\u7684 36 KB \u8fd8\u5728\u961f\u5217\u91cc&#xff0c;\u800c epitem \u5df2\u7ecf\u51fa\u961f&#xff0c;\u5185\u6838\u8bb0\u8d26\u4e3a\u5df2\u901a\u77e5\u3002\u6b64\u540e\u5982\u679c\u5bf9\u7aef\u4e0d\u518d\u53d1\u4efb\u4f55\u6570\u636e&#xff0c;\u8fd9 36 KB \u5c31\u6c38\u8fdc\u8eba\u5728\u90a3\u91cc\u2014\u2014\u5b83\u4f1a\u4e00\u76f4\u8eba\u5230\u8fde\u63a5\u88ab\u5173\u6389\u3002<\/p>\n<p>\u66f4\u9690\u853d\u7684\u662f accept \u4fa7\u3002listen\u00a0fd \u5728 ET \u4e0b\u540c\u6837\u53ea\u5165\u961f\u4e00\u6b21&#xff0c;\u800c accept \u961f\u5217\u91cc\u53ef\u80fd\u4e00\u6b21\u79ef\u4e86\u51e0\u5341\u4e2a\u8fde\u63a5&#xff1a;<\/p>\n<p>C&#043;&#043;<\/p>\n<p>\/\/ \u540c\u6837\u4f1a\u6f0f&#xff0c;\u4e14\u6f0f\u6389\u7684\u662f\u6574\u6761\u8fde\u63a5<br \/>\nif (ev.events &amp; EPOLLIN) {<br \/>\n    int cfd &#061; ::accept4(lfd, nullptr, nullptr, SOCK_NONBLOCK);<br \/>\n    if (cfd &gt;&#061; 0) add_to_epoll(cfd);<br \/>\n}<\/p>\n<p>\u8fd9\u6bb5\u4ee3\u7801\u5728\u4e00\u6b21\u4e8b\u4ef6\u91cc\u53ea\u6458\u8d70\u961f\u9996\u90a3\u4e00\u4e2a\u3002\u5269\u4e0b\u7684\u8fde\u63a5\u7559\u5728 accept \u961f\u5217\u91cc&#xff0c;\u5ba2\u6237\u7aef\u4fa7\u7684\u4e09\u6b21\u63e1\u624b\u5df2\u7ecf\u5b8c\u6210\u4e86\u2014\u2014\u6ce8\u610f\u8fd9\u4e00\u70b9&#xff0c;\u5ba2\u6237\u7aef\u7684\u00a0connect()\u00a0\u65e9\u5c31\u8fd4\u56de\u6210\u529f&#xff0c;\u5b83\u8ba4\u4e3a\u8fde\u63a5\u53ef\u7528&#xff0c;\u5f00\u59cb\u53d1\u6570\u636e&#xff1b;\u670d\u52a1\u7aef\u8fd9\u8fb9\u5185\u6838\u4e5f\u8ba4\u4e3a\u8fde\u63a5\u662f ESTABLISHED&#xff0c;\u53ea\u6709\u4f60\u7684\u8fdb\u7a0b\u5b8c\u5168\u4e0d\u77e5\u9053\u8fd9\u6761\u8fde\u63a5\u7684\u5b58\u5728\u3002\u7b2c\u4e09\u4efd\u526f\u672c\u843d\u540e\u4e8e\u524d\u4e24\u4efd&#xff0c;\u843d\u540e\u65f6\u957f\u53d6\u51b3\u4e8e\u4e0b\u4e00\u6b21\u6709\u65b0\u8fde\u63a5\u5230\u6765\u7684\u65f6\u523b\u3002<\/p>\n<p>\u6b63\u786e\u7684\u5199\u6cd5\u662f\u628a\u300c\u8bfb\u5e72\u51c0\u300d\u5199\u6210\u663e\u5f0f\u5faa\u73af&#xff0c;\u51fa\u53e3\u662f EAGAIN&#xff1a;<\/p>\n<p>C&#043;&#043;<\/p>\n<p>\/\/ ET \u4e0b\u7684\u6536\u655b\u5faa\u73af&#xff1a;\u552f\u4e00\u5408\u6cd5\u7684\u51fa\u53e3\u662f EAGAIN<br \/>\nchar buf[65536];<br \/>\nwhile (true) {<br \/>\n    ssize_t n &#061; ::read(fd, buf, sizeof buf);<br \/>\n    if (n &gt; 0)  { on_data(buf, n); continue; }<br \/>\n    if (n &#061;&#061; 0) { on_peer_fin(fd); break; }        \/\/ \u6536\u5230 FIN<br \/>\n    if (errno &#061;&#061; EINTR)  continue;                  \/\/ \u4fe1\u53f7\u6253\u65ad&#xff0c;\u91cd\u6765<br \/>\n    if (errno &#061;&#061; EAGAIN || errno &#061;&#061; EWOULDBLOCK) break;  \/\/ \u771f\u7684\u8bfb\u5e72\u51c0\u4e86<br \/>\n    on_error(fd, errno); break;<br \/>\n}<\/p>\n<p>\u4e09\u4e2a\u51fa\u53e3\u7684\u8bed\u4e49\u5404\u4e0d\u76f8\u540c&#xff0c;\u6df7\u6dc6\u4efb\u4f55\u4e24\u4e2a\u90fd\u4f1a\u51fa\u4e8b\u3002n &#061;&#061; 0\u00a0\u662f\u5bf9\u7aef\u53d1\u4e86 FIN&#xff0c;\u8fd9\u662f\u72b6\u6001\u53d8\u66f4&#xff1b;EAGAIN\u00a0\u662f\u6682\u65f6\u6ca1\u6570\u636e&#xff0c;\u8fd9\u662f\u6d41\u91cf\u4e8b\u4ef6&#xff1b;\u5176\u4ed6 errno \u662f\u8fde\u63a5\u574f\u4e86\u3002\u6211\u90a3\u53f0\u7f51\u5173\u4e0a\u7684\u6210\u56e0\u5c31\u662f\u7f3a\u4e86\u8fd9\u4e2a\u5faa\u73af&#xff1a;\u4e00\u6b21\u4e8b\u4ef6\u53ea\u8bfb\u4e00\u6b21&#xff0c;\u6570\u636e\u8bfb\u8d70\u4e86&#xff0c;\u7d27\u8ddf\u5728\u6570\u636e\u540e\u9762\u7684\u90a3\u4e2a FIN \u7559\u5728\u961f\u5217\u91cc\u6ca1\u88ab\u53d6\u51fa&#xff0c;n &#061;&#061; 0\u00a0\u8fd9\u6761\u5206\u652f\u4e00\u6b21\u90fd\u6ca1\u8d70\u5230\u8fc7\u3002\u75c7\u72b6\u4e00\u5f52\u4f4d\u3002\u6539\u6210 LT \u4e4b\u6240\u4ee5\u77ed\u6682\u7ba1\u7528&#xff0c;\u662f\u56e0\u4e3a\u5185\u6838\u6bcf\u4e00\u8f6e\u90fd\u628a\u8fd9\u6761 fd \u91cd\u65b0\u585e\u56de\u5c31\u7eea\u961f\u5217&#xff0c;\u90a3\u4e2a FIN \u8fdf\u65e9\u4f1a\u5728\u67d0\u4e00\u8f6e\u88ab\u8bfb\u5230\u2014\u2014\u5b83\u6ca1\u4fee bug&#xff0c;\u53ea\u662f\u8ba9\u5185\u6838\u66ff\u6211\u628a\u5faa\u73af\u8f6c\u5b8c\u4e86\u3002<\/p>\n<p>\u8fd8\u6709\u4e00\u79cd\u66f4\u96be\u7684\u53d8\u4f53&#xff1a;\u5faa\u73af\u5199\u5bf9\u4e86&#xff0c;\u4f46\u00a0n &#061;&#061; 0\u00a0\u88ab\u5e76\u8fdb\u4e86\u00a0EAGAIN\u00a0\u7684\u5206\u652f\u5f53\u6210\u300c\u6682\u65f6\u6ca1\u6570\u636e\u300d\u3002\u8fd9\u4e00\u79cd LT \u4e5f\u6551\u4e0d\u4e86&#xff0c;\u56e0\u4e3a\u65e0\u8bba\u5185\u6838\u901a\u77e5\u591a\u5c11\u6b21&#xff0c;\u90a3\u6761 fd \u4e0a\u6c38\u8fdc\u7b49\u4e0d\u5230\u522b\u7684\u4e1c\u897f\u3002\u5b83\u7684\u66f2\u7ebf\u8ddf\u524d\u4e00\u79cd\u4e00\u6a21\u4e00\u6837&#xff0c;\u9760\u00a0ss\u00a0\u5206\u4e0d\u5f00&#xff0c;\u53ea\u80fd\u8bfb\u4ee3\u7801\u3002<\/p>\n<p>\u8fd9\u91cc\u8fd8\u6709\u4e00\u4e2a\u5fc5\u987b\u914d\u5957\u7684\u7ea6\u675f&#xff1a;ET \u5faa\u73af\u5fc5\u987b\u642d\u914d\u975e\u963b\u585e fd\u3002\u963b\u585e fd \u4e0a\u8fd9\u4e2a\u5faa\u73af\u91cc\u6536\u5c3e\u90a3\u6b21\u00a0read\u00a0\u4f1a\u7761\u8fdb\u53bb&#xff0c;\u628a\u6574\u4e2a\u4e8b\u4ef6\u5faa\u73af\u7ebf\u7a0b\u6302\u4f4f\u3002\u6240\u4ee5\u00a0accept4()\u00a0\u76f4\u63a5\u5e26\u4e0a\u00a0SOCK_NONBLOCK&#xff1b;\u5148 accept \u518d\u00a0fcntl\u00a0\u8bbe\u7f6e\u7684\u5199\u6cd5\u7559\u4e86\u4e00\u4e2a\u7a97\u53e3&#xff0c;\u4ece accept \u8fd4\u56de\u5230\u8bbe\u7f6e\u6210\u529f\u4e4b\u95f4\u90a3\u6761 fd \u662f\u963b\u585e\u7684&#xff0c;\u7a97\u53e3\u5f88\u7a84&#xff0c;\u4f46\u5b83\u5728\u3002<\/p>\n<p>\u5199\u5faa\u73af\u8fd8\u6709\u7b2c\u4e8c\u4e2a\u4ee3\u4ef7&#xff0c;\u5f88\u5c11\u6709\u4eba\u63d0&#xff1a;\u4e00\u4e2a\u75af\u72c2\u53d1\u6570\u636e\u7684\u8fde\u63a5\u4f1a\u628a\u8fd9\u4e2a\u5faa\u73af\u9489\u6b7b&#xff0c;\u4e8b\u4ef6\u5faa\u73af\u91cc\u5176\u4ed6 fd \u62ff\u4e0d\u5230\u8c03\u5ea6\u3002\u6240\u4ee5\u751f\u4ea7\u5b9e\u73b0\u901a\u5e38\u7ed9\u5faa\u73af\u52a0\u4e00\u4e2a\u914d\u989d&#xff0c;\u8bfb\u6ee1 N \u6b21\u5c31\u4e3b\u52a8\u8ba9\u51fa&#xff0c;\u628a\u8fd9\u6761 fd \u8bb0\u8fdb\u4e00\u4e2a\u300c\u5f85\u7eed\u300d\u5217\u8868\u4e0b\u4e00\u8f6e\u4f18\u5148\u5904\u7406\u3002\u8fd9\u7b49\u4e8e\u5728\u5e94\u7528\u5c42\u91cd\u65b0\u5b9e\u73b0\u4e86\u4e00\u904d LT&#xff0c;\u800c\u8fd9\u6070\u597d\u8bf4\u660e\u4e86\u4e00\u4ef6\u4e8b&#xff1a;ET \u4e0e LT \u7684\u5206\u754c\u7ebf\u843d\u5728\u300c\u8c01\u6765\u8bb0\u4f4f\u300e\u8fd8\u6ca1\u8bfb\u5b8c\u300f\u300d\u8fd9\u4e2a\u8d23\u4efb\u4e0a\u3002\u5185\u6838\u8bb0&#xff0c;\u5c31\u662f LT&#xff0c;\u6210\u672c\u662f\u6bcf\u8f6e\u91cd\u67e5&#xff1b;\u4f60\u8bb0&#xff0c;\u5c31\u662f ET&#xff0c;\u6210\u672c\u662f\u8fd9\u6bb5\u5faa\u73af\u548c\u5b83\u7684\u8fb9\u754c\u6761\u4ef6\u3002<\/p>\n<p>\u6211\u7684\u504f\u597d\u662f\u63a5\u5165\u5c42\u7528 ET\u3001\u4e1a\u52a1\u5c42\u7528 LT\u3002\u63a5\u5165\u5c42\u7684 fd \u6570\u91cf\u5927\u3001\u6bcf\u4e2a\u8fde\u63a5\u7684\u6570\u636e\u91cf\u5c0f&#xff0c;LT \u7684\u91cd\u67e5\u6210\u672c\u968f fd \u6570\u7ebf\u6027\u589e\u957f&#xff1b;\u4e1a\u52a1\u5c42\u7684 fd \u5c11\u3001\u5355\u6b21\u6570\u636e\u91cf\u5927\u3001\u903b\u8f91\u590d\u6742&#xff0c;\u628a\u300c\u8bfb\u5e72\u51c0\u300d\u7684\u8d23\u4efb\u4ea4\u7ed9\u5185\u6838\u66f4\u7701\u5fc3\u3002\u8fd9\u4e2a\u504f\u597d\u5728\u6bcf\u8f6e\u5c31\u7eea fd \u6570\u4f4e\u4e8e\u51e0\u767e\u7684\u573a\u666f\u4e0b\u7ad9\u4e0d\u4f4f\u811a\u2014\u2014\u90a3\u65f6\u5019\u4e24\u8005\u7684\u5dee\u522b\u5728\u566a\u58f0\u91cc\u3002<\/p>\n<h3>\u6536\u5230 FIN \u4e4b\u540e&#xff0c;\u90a3\u6761\u8fde\u63a5\u7684\u751f\u547d\u5468\u671f\u5f52\u4f60\u7ba1<\/h3>\n<p>\u88ab\u52a8\u5173\u95ed\u4e00\u4fa7\u7684\u72b6\u6001\u8fc1\u79fb\u53ea\u6709\u4e09\u8df3&#xff1a;ESTABLISHED\u00a0\u6536\u5230\u5bf9\u7aef\u7684 FIN&#xff0c;\u8fdb\u00a0CLOSE_WAIT&#xff1b;\u4f60\u8c03\u00a0close()&#xff0c;\u53d1\u51fa\u81ea\u5df1\u7684 FIN&#xff0c;\u8fdb\u00a0LAST_ACK&#xff1b;\u6536\u5230\u5bf9\u7aef\u7684 ACK&#xff0c;\u8fdb\u00a0CLOSED\u3002<\/p>\n<p>\u4e09\u8df3\u91cc&#xff0c;\u53ea\u6709\u4e2d\u95f4\u90a3\u4e00\u8df3\u9700\u8981\u4f60\u7684\u4ee3\u7801\u3002\u524d\u540e\u4e24\u8df3\u90fd\u662f\u5185\u6838\u6536\u5230\u62a5\u6587\u81ea\u52a8\u5b8c\u6210\u7684\u3002\u6240\u4ee5 CLOSE_WAIT \u7684\u8bed\u4e49\u53ef\u4ee5\u7cbe\u786e\u5230\u4e00\u53e5\u8bdd&#xff1a;\u5185\u6838\u5df2\u7ecf\u786e\u77e5\u5bf9\u7aef\u4e0d\u518d\u53d1\u9001\u6570\u636e&#xff0c;\u5b83\u6b63\u5728\u7b49\u4f60\u7684\u8fdb\u7a0b\u627f\u8ba4\u8fd9\u4ef6\u4e8b\u3002<\/p>\n<p>\u5148\u628a\u4e00\u4e2a\u5e38\u89c1\u7684\u56f0\u60d1\u5904\u7406\u6389&#xff1a;\u4e3a\u4ec0\u4e48 CLOSE_WAIT \u6ca1\u6709\u8d85\u65f6&#xff0c;\u800c\u5bf9\u79f0\u4f4d\u7f6e\u4e0a\u7684 FIN_WAIT_2 \u6709\u3002<\/p>\n<p>FIN_WAIT_2 \u662f\u4e3b\u52a8\u5173\u95ed\u65b9\u53d1\u5b8c FIN\u3001\u6536\u5230 ACK \u4e4b\u540e\u7684\u7b49\u5f85\u6001&#xff0c;\u5b83\u7b49\u7684\u662f\u5bf9\u7aef\u5e94\u7528\u8c03\u00a0close()\u3002include\/net\/tcp.h\u00a0\u91cc\u7684\u5e38\u91cf\u7ed9\u4e86\u5b83\u4e00\u4e2a\u4e0a\u9650&#xff1a;<\/p>\n<p>C<\/p>\n<p>\/* include\/net\/tcp.h, Linux 6.6 *\/<br \/>\n#define TCP_TIMEWAIT_LEN (60*HZ) \/* how long to wait to destroy TIME-WAIT<br \/>\n                                  * state, about 60 seconds *\/<br \/>\n#define TCP_FIN_TIMEOUT  TCP_TIMEWAIT_LEN<\/p>\n<p>tcp_fin_timeout\u00a0\u7684\u6587\u6863\u5199\u5f97\u5f88\u514b\u5236&#xff0c;\u5173\u952e\u9650\u5b9a\u8bcd\u5728\u5f00\u5934&#xff1a;\u300cThe length of time an\u00a0orphaned&#xff08;no longer referenced by any application&#xff09;connection will remain in the FIN_WAIT_2 state before it is aborted at the local end. Default: 60 seconds\u300d\u3002\u5b64\u513f\u8fde\u63a5\u624d\u6709\u8d85\u65f6\u3002\u90a3\u6761\u8fde\u63a5\u7684 fd \u5df2\u7ecf\u88ab\u5e94\u7528\u91ca\u653e\u4e86&#xff0c;\u5185\u6838\u6210\u4e86\u5b83\u552f\u4e00\u7684\u6301\u6709\u8005&#xff0c;\u4e8e\u662f\u5185\u6838\u6709\u6743\u5904\u7f6e\u5b83\u3002<\/p>\n<p>CLOSE_WAIT \u7684\u60c5\u51b5\u6b63\u76f8\u53cd&#xff1a;fd \u8fd8\u5728\u4f60\u624b\u91cc\u3002TCP \u5141\u8bb8\u534a\u5173\u95ed\u2014\u2014\u5bf9\u7aef\u8bf4\u300c\u6211\u53d1\u5b8c\u4e86\u300d&#xff0c;\u5b8c\u5168\u4e0d\u7b49\u4e8e\u300c\u6211\u4e0d\u6536\u4e86\u300d\u3002\u5b83\u53ef\u80fd\u6b63\u7b49\u7740\u4f60\u628a\u8ba1\u7b97\u7ed3\u679c\u5199\u56de\u53bb\u3002\u5185\u6838\u5982\u679c\u7ed9 CLOSE_WAIT \u52a0\u4e00\u4e2a\u8d85\u65f6&#xff0c;\u7b49\u4e8e\u66ff\u4f60\u51b3\u5b9a\u4e86\u300c\u8fd9\u4e2a\u65b9\u5411\u4e5f\u8be5\u5173\u300d&#xff0c;\u800c\u8fd9\u4e2a\u51b3\u5b9a\u6807\u51c6\u91cc\u6ca1\u6709\u6388\u6743\u7ed9\u5b83\u3002CLOSE_WAIT \u6c38\u4e0d\u6d88\u9000\u662f\u8bed\u4e49\u7684\u5fc5\u7136\u7ed3\u679c&#xff0c;\u628a\u5b83\u5f53\u6210\u5185\u6838\u7684\u7f3a\u9677\u4f1a\u4e00\u8def\u6392\u67e5\u5230\u9519\u7684\u5730\u65b9\u3002<\/p>\n<p>\u534a\u5173\u95ed\u7684\u4e24\u4e2a\u63a5\u53e3\u503c\u5f97\u5206\u6e05\u695a&#xff0c;\u5b83\u4eec\u7684\u5bf9\u79f0\u6027\u662f\u5047\u7684&#xff1a;<\/p>\n<p>C&#043;&#043;<\/p>\n<p>::shutdown(fd, SHUT_WR);   \/\/ \u771f\u7684\u53d1\u51fa FIN&#xff0c;\u5bf9\u7aef read \u4f1a\u8fd4\u56de 0<br \/>\n::shutdown(fd, SHUT_RD);   \/\/ \u672c\u5730\u6807\u8bb0&#xff0c;\u4e0d\u53d1\u4efb\u4f55\u62a5\u6587<br \/>\n::close(fd);               \/\/ \u5f15\u7528\u8ba1\u6570\u5f52\u96f6\u65f6\u624d\u53d1 FIN<\/p>\n<p>SHUT_WR\u00a0\u662f\u4e00\u4e2a\u534f\u8bae\u52a8\u4f5c&#xff0c;\u5b83\u628a\u300c\u6211\u4e0d\u518d\u53d1\u9001\u300d\u8fd9\u6761\u4fe1\u606f\u540c\u6b65\u7ed9\u4e86\u5bf9\u7aef\u5185\u6838\u3002SHUT_RD\u00a0\u53ea\u662f\u672c\u5730\u628a\u8bfb\u65b9\u5411\u6807\u6b7b&#xff0c;\u540e\u7eed\u00a0read\u00a0\u8fd4\u56de 0&#xff0c;\u7ebf\u4e0a\u4ec0\u4e48\u90fd\u6ca1\u53d1\u751f&#xff0c;\u5bf9\u7aef\u6beb\u4e0d\u77e5\u60c5\u3002close()\u00a0\u5219\u53d7\u5f15\u7528\u8ba1\u6570\u7ea6\u675f&#xff1a;fork()\u00a0\u4e4b\u540e\u7236\u5b50\u8fdb\u7a0b\u5404\u6301\u4e00\u4efd\u3001\u6216\u8005\u00a0dup()\u00a0\u8fc7\u7684 fd&#xff0c;\u5176\u4e2d\u4e00\u4e2a\u00a0close()\u00a0\u4e0d\u4f1a\u53d1 FIN\u3002\u6211\u6392\u67e5\u8fc7\u4e00\u6b21 CLOSE_WAIT \u5806\u79ef&#xff0c;\u4ee3\u7801\u91cc\u00a0close()\u00a0\u8c03\u5f97\u89c4\u89c4\u77e9\u77e9&#xff0c;\u6210\u56e0\u662f\u4e00\u4e2a\u65e9\u671f\u7248\u672c\u7559\u4e0b\u7684\u00a0dup()&#xff0c;\u53e6\u4e00\u4efd fd \u5b58\u5728\u4e00\u4e2a\u518d\u4e5f\u6ca1\u88ab\u8bbf\u95ee\u8fc7\u7684 map \u91cc\u3002<\/p>\n<p>\u6700\u5bb9\u6613\u88ab\u6f0f\u6389\u7684\u662f\u00a0close()\u00a0\u7684\u53e6\u4e00\u6761\u5206\u652f&#xff1a;\u5b83\u4e0d\u4e00\u5b9a\u53d1 FIN\u3002net\/ipv4\/tcp.c\u00a0\u7684\u00a0__tcp_close()\u00a0\u5f00\u5934\u4f1a\u628a\u63a5\u6536\u961f\u5217\u6392\u7a7a\u5e76\u8ba1\u7b97\u672a\u8bfb\u5b57\u8282\u6570&#xff1a;<\/p>\n<p>C<\/p>\n<p>\/* net\/ipv4\/tcp.c, Linux 6.6, __tcp_close() *\/<br \/>\nwhile ((skb &#061; __skb_dequeue(&amp;sk-&gt;sk_receive_queue)) !&#061; NULL) {<br \/>\n    u32 len &#061; TCP_SKB_CB(skb)-&gt;end_seq &#8211; TCP_SKB_CB(skb)-&gt;seq;<\/p>\n<p>    if (TCP_SKB_CB(skb)-&gt;tcp_flags &amp; TCPHDR_FIN)<br \/>\n        len&#8211;;<br \/>\n    data_was_unread &#043;&#061; len;<br \/>\n    __kfree_skb(skb);<br \/>\n}<\/p>\n<p>\u5982\u679c\u00a0data_was_unread\u00a0\u5927\u4e8e\u96f6&#xff0c;\u8d70\u7684\u662f\u53e6\u4e00\u6761\u8def&#xff0c;\u6ce8\u91ca\u91cc\u8fde\u5e26\u8bb0\u4e86\u4e00\u6bb5 1990 \u5e74\u4ee3\u7684\u6545\u969c\u73b0\u573a&#xff1a;<\/p>\n<p>C<\/p>\n<p>\/* As outlined in RFC 2525, section 2.17, we send a RST here because<br \/>\n * data was lost. To witness the awful effects of the old behavior of<br \/>\n * always doing a FIN, run an older 2.1.x kernel or 2.0.x, start a bulk<br \/>\n * GET in an FTP client, suspend the process, wait for the client to<br \/>\n * advertise a zero window, then kill -9 the FTP client, wheee&#8230;<br \/>\n *\/<\/p>\n<p>\u7d27\u63a5\u7740\u662f\u00a0tcp_set_state(sk, TCP_CLOSE)\u00a0\u52a0\u00a0tcp_send_active_reset()&#xff0c;\u5e76\u4e14\u8ba1\u6570\u5230\u00a0LINUX_MIB_TCPABORTONCLOSE\u3002\u8fd9\u4e2a\u8ba1\u6570\u5668\u5728\u00a0netstat -s\u00a0\u7684 TcpExt \u6bb5\u91cc\u663e\u793a\u6210\u00a0connections reset due to early user close&#xff0c;\u5b83\u662f\u6392\u67e5\u300c\u5bf9\u7aef\u5076\u53d1 ECONNRESET\u300d\u65f6\u7b2c\u4e00\u4e2a\u8be5\u770b\u7684\u6570\u3002\u76f8\u90bb\u90a3\u4e2a\u00a0connections reset due to unexpected data\u00a0\u662f\u00a0TCPAbortOnData&#xff0c;\u8bb0\u7684\u662f\u53e6\u4e00\u4ef6\u4e8b\u2014\u2014\u8fde\u63a5\u5df2\u7ecf\u5728\u5173\u95ed\u6d41\u7a0b\u91cc&#xff08;FIN_WAIT \u72b6\u6001&#xff09;\u53c8\u6536\u5230\u4e86\u6570\u636e&#xff0c;\u4e24\u4e2a\u6570\u522b\u770b\u6df7\u3002<\/p>\n<p>\u63a8\u8bba\u5bf9\u5199\u670d\u52a1\u7aef\u7684\u4eba\u5f88\u5b9e\u9645&#xff1a;\u4f60\u7684\u8fdb\u7a0b\u5728\u5173\u8fde\u63a5\u4e4b\u524d\u6709\u6ca1\u6709\u628a\u63a5\u6536\u961f\u5217\u8bfb\u5e72\u51c0&#xff0c;\u51b3\u5b9a\u4e86\u5bf9\u7aef\u6536\u5230\u7684\u662f FIN \u8fd8\u662f RST\u3002\u00a0\u6536\u5230 FIN&#xff0c;\u5bf9\u7aef\u80fd\u5b8c\u6210\u6b63\u5e38\u7684\u5173\u95ed\u6d41\u7a0b&#xff0c;\u5728\u9014\u6570\u636e\u4e0d\u4f1a\u4e22&#xff1b;\u6536\u5230 RST&#xff0c;\u5bf9\u7aef\u5185\u6838\u4f1a\u4e22\u5f03\u81ea\u5df1\u63a5\u6536\u961f\u5217\u91cc\u5c1a\u672a\u4ea4\u4ed8\u7ed9\u5e94\u7528\u7684\u6570\u636e&#xff0c;read\u00a0\u76f4\u63a5\u8fd4\u56de\u00a0ECONNRESET\u3002\u4e00\u4e2a\u4e1a\u52a1\u4fa7\u300c\u6211\u5df2\u7ecf\u5904\u7406\u5b8c\u4e86\u4e3b\u52a8\u65ad\u5f00\u300d\u7684\u4f18\u5316&#xff0c;\u914d\u4e0a\u6ca1\u8bfb\u5e72\u51c0\u7684\u63a5\u6536\u961f\u5217&#xff0c;\u8868\u73b0\u5c31\u662f\u5bf9\u7aef\u96f6\u661f\u4e22\u8bf7\u6c42&#xff0c;\u800c\u6293\u5305\u770b\u4e24\u7aef\u65f6\u5e8f\u5b8c\u5168\u6b63\u5e38\u2014\u2014RST \u662f\u5408\u6cd5\u62a5\u6587&#xff0c;\u5b83\u53ea\u662f\u628a\u6570\u636e\u5e26\u8d70\u4e86\u3002<\/p>\n<p>SO_LINGER\u00a0\u8bbe\u6210\u00a0l_onoff &#061; 1, l_linger &#061; 0\u00a0\u662f\u663e\u5f0f\u8d70\u8fd9\u6761\u8def&#xff0c;\u5185\u6838\u91cc\u90a3\u6bb5\u5224\u65ad\u7d27\u8ddf\u5728\u00a0data_was_unread\u00a0\u4e4b\u540e&#xff1a;<\/p>\n<p>C<\/p>\n<p>} else if (sock_flag(sk, SOCK_LINGER) &amp;&amp; !sk-&gt;sk_lingertime) {<br \/>\n    \/* Check zero linger _after_ checking for unread data. *\/<br \/>\n    sk-&gt;sk_prot-&gt;disconnect(sk, 0);<br \/>\n    NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTONDATA);<br \/>\n}<\/p>\n<p>\u6ce8\u91ca\u91cc\u90a3\u53e5\u00a0Check zero linger _after_ checking for unread data\u00a0\u8bf4\u660e\u4e86\u4f18\u5148\u7ea7&#xff1a;\u6709\u672a\u8bfb\u6570\u636e\u65f6\u6309 RFC 2525 \u53d1 RST&#xff0c;\u4e24\u6761\u8def\u6b8a\u9014\u540c\u5f52&#xff0c;\u4f46\u8ba1\u6570\u5668\u4e0d\u540c&#xff0c;\u4e00\u4e2a\u8bb0\u00a0TCPABORTONCLOSE&#xff0c;\u4e00\u4e2a\u8bb0\u00a0TCPABORTONDATA\u3002\u6392\u67e5\u65f6\u8fd9\u4e24\u4e2a\u6570\u80fd\u628a\u8d23\u4efb\u5206\u6e05\u695a&#xff0c;\u503c\u5f97\u5355\u72ec\u76ef\u3002<\/p>\n<h3>TIME_WAIT \u90a3\u516d\u5341\u79d2&#xff0c;\u5185\u6838\u66ff\u5bf9\u7aef\u7559\u7740\u4e00\u4e2a\u80fd\u56de ACK \u7684\u4eba<\/h3>\n<p>\u628a CLOSE_WAIT \u548c TIME_WAIT \u6446\u5728\u4e00\u8d77\u770b&#xff0c;\u5b83\u4eec\u7684\u5f62\u72b6\u6781\u50cf&#xff1a;\u90fd\u662f\u300c\u8fde\u63a5\u903b\u8f91\u4e0a\u5df2\u7ecf\u7ed3\u675f&#xff0c;\u5185\u6838\u4ecd\u5728\u5185\u5b58\u91cc\u7559\u7740\u4e00\u4efd\u72b6\u6001\u300d\u3002\u7b49\u7684\u5bf9\u8c61\u5374\u5b8c\u5168\u76f8\u53cd&#xff0c;\u800c\u8fd9\u4e2a\u76f8\u53cd\u51b3\u5b9a\u4e86\u4e24\u79cd\u5806\u79ef\u7684\u6392\u67e5\u65b9\u5411\u622a\u7136\u4e0d\u540c\u3002<\/p>\n<p>CLOSE_WAIT \u7b49\u7684\u662f\u672c\u673a\u7684\u8fdb\u7a0b\u3002TIME_WAIT \u7b49\u7684\u662f\u5bf9\u7aef\u5185\u6838\u7684\u91cd\u4f20\u3002<\/p>\n<p>\u5185\u6838\u6ce8\u91ca\u628a\u7b2c\u4e8c\u4ef6\u4e8b\u8bb2\u5f97\u6bd4\u4efb\u4f55\u6559\u79d1\u4e66\u90fd\u76f4\u63a5\u3002net\/ipv4\/tcp_minisocks.c\u00a0\u91cc\u00a0tcp_timewait_state_process()\u00a0\u4e0a\u65b9\u90a3\u6bb5&#xff1a;<\/p>\n<p>text<\/p>\n<p>Main purpose of TIME-WAIT state is to close connection<br \/>\ngracefully, when one of ends sits in LAST-ACK or<br \/>\nCLOSING retransmitting FIN (and, probably, tail of<br \/>\ndata) and one or more our ACKs are lost.<br \/>\n&#8230;<br \/>\nSecond purpose of TIME-WAIT is catching old duplicate<br \/>\nsegments. Well, certainly it is pure paranoia, but if<br \/>\nwe load TIME-WAIT with this semantics, we MUST NOT<br \/>\nkill TIME-WAIT state with RSTs.<\/p>\n<p>\u591a\u6570\u4e2d\u6587\u8d44\u6599\u8bb2 TIME_WAIT \u65f6&#xff0c;\u5f00\u7bc7\u5c31\u662f\u300c\u9632\u6b62\u65e7\u8fde\u63a5\u7684\u62a5\u6587\u5e72\u6270\u65b0\u8fde\u63a5\u300d\u3002\u90a3\u662f\u5185\u6838\u4f5c\u8005\u6807\u6ce8\u7684\u7b2c\u4e8c\u76ee\u7684&#xff0c;\u800c\u4e14\u4ed6\u5728\u65c1\u8fb9\u5199\u4e86\u00a0pure paranoia\u3002\u7b2c\u4e00\u76ee\u7684\u662f\u522b\u7684\u4e1c\u897f&#xff1a;\u5bf9\u7aef\u6b64\u523b\u53ef\u80fd\u5361\u5728 LAST_ACK \u91cc\u53cd\u590d\u91cd\u4f20 FIN&#xff0c;\u6211\u8fd9\u8fb9\u56de\u7684\u90a3\u4e2a\u6536\u5c3e ACK \u4e00\u65e6\u4e22\u4e86&#xff0c;\u5f97\u6709\u4eba\u5728\u8fd9\u4e2a\u56db\u5143\u7ec4\u4e0a\u518d\u56de\u4e00\u6b21\u3002TIME_WAIT \u662f\u4e3a\u5bf9\u7aef\u90a3\u4efd\u72b6\u6001\u526f\u672c\u7559\u7684\u515c\u5e95\u4eba\u3002\u00a0\u5b83\u8ddf\u672c\u7aef\u7684\u4e1a\u52a1\u6beb\u65e0\u5173\u7cfb&#xff0c;\u672c\u7aef\u4ed8\u51fa\u7684\u662f\u5185\u5b58\u548c\u7aef\u53e3\u5360\u7528&#xff0c;\u6536\u76ca\u5168\u90e8\u5f52\u5bf9\u7aef\u3002<\/p>\n<p>\u7406\u89e3\u4e86\u8fd9\u4e00\u70b9&#xff0c;\u51e0\u4e2a\u957f\u5e74\u88ab\u5f53\u6210\u300c\u8c03\u53c2\u6280\u5de7\u300d\u7684\u4e1c\u897f\u5c31\u6709\u4e86\u5224\u636e\u3002<\/p>\n<p>\u4e3a\u4ec0\u4e48\u662f\u516d\u5341\u79d2\u3002\u00a0\u4e0a\u9762\u90a3\u4e2a\u00a0TCP_TIMEWAIT_LEN\u00a0\u662f\u4e00\u4e2a\u7f16\u8bd1\u671f\u5e38\u91cf&#xff0c;tcp_time_wait()\u00a0\u91cc\u5bf9\u8fdb\u5165 TIME_WAIT \u7684\u8fde\u63a5\u76f4\u63a5\u8d4b\u503c\u00a0timeo &#061; TCP_TIMEWAIT_LEN\u3002\u6559\u79d1\u4e66\u8bf4 2MSL\u3001MSL \u53d6\u51b3\u4e8e\u5b9e\u73b0&#xff0c;Linux \u628a\u5b83\u9489\u6b7b\u5728\u516d\u5341\u79d2&#xff0c;\/proc\u00a0\u4e0b\u6ca1\u6709\u5bf9\u5e94\u7684\u53ef\u8c03\u9879\u3002tcp_fin_timeout\u00a0\u5e38\u88ab\u8bef\u5f53\u6210 TIME_WAIT \u7684\u65f6\u957f&#xff0c;\u5b83\u7ba1\u7684\u662f FIN_WAIT_2&#xff0c;\u53ea\u662f\u6070\u597d\u5171\u7528\u4e86\u540c\u4e00\u4e2a\u5e38\u91cf\u3002\u8fd9\u4e00\u6761\u5728\u751f\u4ea7\u4e0a\u5f88\u5b9e\u9645&#xff1a;\u60f3\u7f29\u77ed TIME_WAIT&#xff0c;\u6539\u5185\u6838\u53c2\u6570\u8fd9\u6761\u8def\u8d70\u4e0d\u901a&#xff0c;\u53ea\u80fd\u6539\u8fde\u63a5\u6a21\u5f0f\u6216\u8005\u91cd\u7f16\u5185\u6838\u3002<\/p>\n<p>\u4e3a\u4ec0\u4e48\u4e3b\u52a8\u5173\u95ed\u65b9\u624d\u8fdb TIME_WAIT\u3002\u00a0\u8c01\u5148\u53d1 FIN&#xff0c;\u8c01\u5c31\u8981\u4e3a\u90a3\u4e2a\u7ec8\u7ed3\u6027\u7684 ACK \u515c\u5e95\u3002\u6240\u4ee5\u670d\u52a1\u7aef\u4e3b\u52a8\u5173\u77ed\u8fde\u63a5&#xff0c;TIME_WAIT \u5168\u5806\u5728\u670d\u52a1\u7aef&#xff0c;\u6bcf\u6761\u5360\u4e00\u4e2a\u56db\u5143\u7ec4&#xff1b;\u53cd\u8fc7\u6765\u8ba9\u5ba2\u6237\u7aef\u4e3b\u52a8\u5173&#xff0c;\u538b\u529b\u5206\u644a\u5230\u6210\u5343\u4e0a\u4e07\u4e2a\u5ba2\u6237\u7aef\u4e0a&#xff0c;\u6bcf\u4e2a\u90fd\u53ea\u6709\u51e0\u6761\u3002\u8fd9\u662f\u6211\u89c1\u8fc7\u7684\u77ed\u8fde\u63a5\u67b6\u6784\u91cc\u6700\u503c\u94b1\u7684\u4e00\u6761\u8bbe\u8ba1\u7ea6\u675f&#xff0c;\u5b83\u51b3\u5b9a\u4e86\u670d\u52a1\u7aef\u8981\u4e0d\u8981\u4e3a\u7aef\u53e3\u8017\u5c3d\u505a\u51c6\u5907\u3002<\/p>\n<p>tcp_tw_reuse\u00a0\u7684\u9ed8\u8ba4\u503c\u53d8\u8fc7\u3002\u00a0\u73b0\u5728\u7684\u6587\u6863\u5199\u7684\u662f&#xff1a;\u300c0 &#8211; disable&#xff0c;1 &#8211; global enable&#xff0c;2 &#8211; enable for loopback traffic only.\u00a0Default: 2\u300d\u3002\u5f88\u591a\u6d41\u4f20\u7684\u8c03\u4f18\u811a\u672c\u91cc\u5199\u7740\u00a0net.ipv4.tcp_tw_reuse &#061; 1&#xff0c;\u90a3\u662f\u5728\u9ed8\u8ba4\u503c\u8fd8\u662f 0 \u7684\u5e74\u4ee3\u5199\u7684\u3002\u73b0\u5728\u7684\u9ed8\u8ba4\u503c\u5df2\u7ecf\u8986\u76d6\u4e86\u7edd\u5927\u591a\u6570\u771f\u5b9e\u75db\u70b9\u2014\u2014\u672c\u673a\u56de\u73af\u4e0a\u7684\u77ed\u8fde\u63a5\u2014\u2014\u800c\u628a\u5b83\u5168\u5c40\u6253\u5f00\u6d89\u53ca\u8de8\u673a\u7684\u65e7\u62a5\u6587\u98ce\u9669&#xff0c;\u5185\u6838\u9009\u62e9\u4e86\u4fdd\u5b88\u3002\u53e6\u5916&#xff0c;tcp_tw_recycle\u00a0\u5728 4.12 \u4e4b\u540e\u5df2\u7ecf\u4ece\u5185\u6838\u91cc\u5220\u6389\u4e86&#xff0c;\u8fd8\u5728\u5efa\u8bae\u5f00\u8fd9\u4e2a\u53c2\u6570\u7684\u6587\u7ae0&#xff0c;\u5e74\u4efd\u53ef\u4ee5\u76f4\u63a5\u770b\u51fa\u6765\u3002<\/p>\n<p>tcp_max_tw_buckets\u00a0\u662f\u4e2a\u786c\u622a\u65ad\u3002\u00a0\u6587\u6863\u539f\u8bdd&#xff1a;\u300cMaximal number of timewait sockets held by system simultaneously. If this number is exceeded time-wait socket is immediately destroyed and warning is printed.\u300d\u8d85\u4e86\u5c31\u76f4\u63a5\u9500\u6bc1\u5e76\u6253\u65e5\u5fd7\u3002\u628a\u5b83\u8c03\u5c0f\u786e\u5b9e\u80fd\u538b\u4f4f TIME_WAIT \u8ba1\u6570&#xff0c;\u4ee3\u4ef7\u662f\u4f60\u4e3b\u52a8\u653e\u5f03\u4e86\u7ed9\u5bf9\u7aef\u515c\u5e95\u7684\u4e49\u52a1&#xff0c;\u6362\u6765\u7684\u662f\u5bf9\u7aef\u90a3\u4fa7\u5076\u53d1\u7684\u00a0Connection reset\u3002\u8fd9\u4e2a\u5f00\u5173\u5f88\u5c11\u662f\u5bf9\u7684\u9009\u62e9&#xff0c;\u9664\u975e\u4f60\u5df2\u7ecf\u786e\u8ba4\u5bf9\u7aef\u7684\u91cd\u4f20\u8def\u5f84\u4e0d\u5b58\u5728\u3002<\/p>\n<p>SO_REUSEADDR\u00a0\u89e3\u51b3\u7684\u662f\u53e6\u4e00\u4e2a\u95ee\u9898\u3002\u00a0\u5b83\u8ba9\u00a0bind()\u00a0\u80fd\u7ed1\u4e0a\u4e00\u4e2a\u4ecd\u5904\u5728 TIME_WAIT \u7684\u672c\u5730\u5730\u5740&#xff0c;\u4f5c\u7528\u8303\u56f4\u662f\u672c\u8fdb\u7a0b\u7684\u76d1\u542c\u7aef\u53e3&#xff0c;\u8ddf\u8fde\u63a5\u6570\u91cf\u65e0\u5173\u3002\u670d\u52a1\u7aef\u91cd\u542f\u65f6\u7684\u00a0Address already in use&#xff0c;\u7edd\u5927\u591a\u6570\u662f\u8fd9\u4e2a\u5f00\u5173\u7684\u4e8b\u3002\u5b83\u8ddf\u00a0tcp_tw_reuse\u00a0\u540d\u5b57\u50cf&#xff0c;\u7ba1\u7684\u4e1c\u897f\u5b8c\u5168\u4e0d\u540c&#xff1a;\u4e00\u4e2a\u7ba1 bind&#xff0c;\u4e00\u4e2a\u7ba1\u53d1\u8d77\u65b0\u8fde\u63a5\u65f6\u80fd\u5426\u590d\u7528\u5904\u5728 TIME_WAIT \u7684\u56db\u5143\u7ec4\u3002<\/p>\n<p>\u56de\u5230\u75c7\u72b6\u3002\u90a3\u53f0\u7f51\u5173\u4e0a\u7684 TIME_WAIT \u4e5f\u5728\u6da8&#xff0c;\u4f46\u5b83\u6da8\u5f97\u5e73\u7a33\u3001\u6709\u4e0a\u754c&#xff0c;\u8ddf CLOSE_WAIT \u7684\u5355\u8c03\u722c\u5347\u662f\u4e24\u6761\u66f2\u7ebf\u3002TIME_WAIT \u5806\u79ef\u662f\u8fde\u63a5\u6a21\u5f0f\u7684\u8bfb\u6570&#xff0c;CLOSE_WAIT \u5806\u79ef\u662f\u5e94\u7528\u4ee3\u7801\u7684\u8bfb\u6570&#xff0c;\u628a\u5b83\u4eec\u653e\u8fdb\u540c\u4e00\u5f20\u544a\u8b66\u91cc\u770b&#xff0c;\u662f\u6211\u5f53\u65f6\u5224\u65ad\u8dd1\u504f\u7684\u539f\u56e0\u4e4b\u4e00\u3002<\/p>\n<h3>\u5efa\u7acb\u8981\u4e09\u6b65\u800c\u62c6\u9664\u8981\u56db\u6b65&#xff0c;\u5dee\u7684\u662f\u90a3\u4e2a\u65b9\u5411<\/h3>\n<p>\u63e1\u624b\u4e0e\u6325\u624b\u7684\u6b21\u6570\u5dee&#xff0c;\u51e0\u4e4e\u6bcf\u4efd\u8d44\u6599\u90fd\u4f1a\u8bb2&#xff0c;\u8bb2\u6cd5\u901a\u5e38\u662f\u300c\u56e0\u4e3a FIN \u548c ACK \u4e0d\u80fd\u5408\u5e76\u300d\u3002\u8fd9\u662f\u7ed3\u8bba&#xff0c;\u4e0d\u662f\u7406\u7531\u3002<\/p>\n<p>\u56de\u5230\u526f\u672c\u6a21\u578b\u63a8\u4e00\u904d\u3002\u5efa\u7acb\u8fde\u63a5\u8981\u540c\u6b65\u7684\u4e1c\u897f\u662f\u4e24\u4e2a\u65b9\u5411\u5404\u81ea\u7684\u8d77\u59cb\u5e8f\u53f7\u3002A \u544a\u8bc9 B \u81ea\u5df1\u7684 ISN&#xff0c;B \u786e\u8ba4&#xff1b;B \u544a\u8bc9 A \u81ea\u5df1\u7684 ISN&#xff0c;A \u786e\u8ba4\u3002\u56db\u4e2a\u52a8\u4f5c\u3002\u4e2d\u95f4\u90a3\u4e24\u4e2a\u52a8\u4f5c\u2014\u2014B \u5bf9 A \u7684\u786e\u8ba4\u3001B \u5bf9\u81ea\u5df1 ISN \u7684\u5ba3\u544a\u2014\u2014\u53d1\u751f\u5728\u540c\u4e00\u65f6\u523b\u3001\u540c\u4e00\u53f0\u673a\u5668\u4e0a\u3001\u9762\u5411\u540c\u4e00\u4e2a\u5bf9\u7aef&#xff0c;\u6ca1\u6709\u4efb\u4f55\u7406\u7531\u5206\u6210\u4e24\u4e2a\u5305&#xff0c;\u4e8e\u662f\u5408\u5e76\u6210 SYN&#043;ACK&#xff0c;\u56db\u6b65\u538b\u6210\u4e09\u6b65\u3002<\/p>\n<p>\u62c6\u9664\u8fde\u63a5\u8981\u540c\u6b65\u7684\u4e1c\u897f\u662f\u4e24\u4e2a\u65b9\u5411\u5404\u81ea\u7684\u7ed3\u675f\u3002A \u8bf4\u300c\u6211\u53d1\u5b8c\u4e86\u300d&#xff0c;B \u786e\u8ba4&#xff1b;B \u8bf4\u300c\u6211\u53d1\u5b8c\u4e86\u300d&#xff0c;A \u786e\u8ba4\u3002\u540c\u6837\u662f\u56db\u4e2a\u52a8\u4f5c\u3002\u4e2d\u95f4\u90a3\u4e24\u4e2a\u52a8\u4f5c\u5374\u4e0d\u5728\u540c\u4e00\u65f6\u523b&#xff1a;B \u6536\u5230 A \u7684 FIN \u65f6&#xff0c;B \u7684\u5e94\u7528\u53ef\u80fd\u8fd8\u6709\u534a\u4e2a\u54cd\u5e94\u6ca1\u5199\u5b8c\u3002\u5185\u6838\u6536\u5230 FIN \u5fc5\u987b\u7acb\u523b\u786e\u8ba4&#xff0c;\u5426\u5219 A \u4f1a\u91cd\u4f20&#xff1b;\u800c\u300c\u6211\u4e5f\u53d1\u5b8c\u4e86\u300d\u8fd9\u4ef6\u4e8b\u8981\u7b49 B \u7684\u5e94\u7528\u8c03\u00a0close()&#xff0c;\u53ef\u80fd\u662f\u51e0\u5fae\u79d2\u540e&#xff0c;\u4e5f\u53ef\u80fd\u662f\u51e0\u5206\u949f\u540e\u3002\u4e2d\u95f4\u90a3\u6bb5\u65e0\u6cd5\u9884\u6d4b\u7684\u95f4\u9694&#xff0c;\u5c31\u662f CLOSE_WAIT \u72b6\u6001\u672c\u8eab\u3002\u00a0\u5408\u5e76\u4e0d\u4e86\u7684\u539f\u56e0\u5728\u8fd9\u91cc&#xff0c;\u8ddf\u62a5\u6587\u683c\u5f0f\u65e0\u5173\u3002<\/p>\n<p>\u5f53 B \u7684\u5e94\u7528\u786e\u5b9e\u6ca1\u6709\u4efb\u4f55\u5f85\u53d1\u6570\u636e\u3001\u4e14 delayed ACK \u8fd8\u6ca1\u89e6\u53d1\u65f6&#xff0c;Linux \u4f1a\u628a FIN \u548c ACK \u5408\u5e76&#xff0c;\u6293\u5305\u80fd\u770b\u5230\u4e09\u6b21\u6325\u624b\u3002\u5b83\u662f\u4f18\u5316\u7684\u7ed3\u679c&#xff0c;\u4e0d\u662f\u534f\u8bae\u89c4\u5b9a\u7684\u5f62\u6001\u3002<\/p>\n<p>\u534a\u5f00\u8fde\u63a5\u662f\u540c\u4e00\u679a\u786c\u5e01\u7684\u53e6\u4e00\u9762\u3002RFC 9293 \u00a73.5.1 \u7684\u63aa\u8f9e\u524d\u9762\u5f15\u8fc7&#xff0c;without the knowledge of the other\u3002\u6807\u51c6\u63a5\u7740\u5199&#xff1a;\u8fd9\u7c7b\u8fde\u63a5\u300cwill automatically become reset if an attempt is made to send data in either direction\u300d\u2014\u2014\u53ea\u8981\u4efb\u4e00\u65b9\u5411\u5c1d\u8bd5\u53d1\u6570\u636e&#xff0c;\u5b83\u5c31\u4f1a\u88ab\u81ea\u52a8\u91cd\u7f6e\u3002\u6062\u590d\u673a\u5236\u662f\u6709\u7684&#xff0c;\u89e6\u53d1\u6761\u4ef6\u662f\u53d1\u6570\u636e\u3002\u00a0\u4e00\u6761\u7a7a\u95f2\u7684\u534a\u5f00\u8fde\u63a5&#xff0c;\u53ef\u4ee5\u5728\u4e24\u7aef\u7684\u5185\u5b58\u91cc\u5404\u8eba\u5404\u7684&#xff0c;\u8eba\u5230\u8fdb\u7a0b\u9000\u51fa\u3002<\/p>\n<p>\u5efa\u7acb\u4fa7\u8fd8\u6709\u4e00\u4e2a\u88ab\u5e7f\u6cdb\u8bb2\u9519\u7684\u5730\u65b9&#xff1a;listen()\u00a0\u7684 backlog \u5230\u5e95\u662f\u4ec0\u4e48\u3002\u5185\u6838\u7ef4\u62a4\u7684\u662f\u4e24\u4e2a\u961f\u5217\u3002<\/p>\n<p>text<\/p>\n<p>   SYN \u5230\u8fbe<br \/>\n      \u2502<br \/>\n      \u25bc<br \/>\n \u250c\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2510   \u6536\u5230 ACK   \u250c\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2510<br \/>\n \u2502  SYN \u961f\u5217       \u2502 \u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u25ba \u2502  accept \u961f\u5217    \u2502<br \/>\n \u2502 (SYN_RECV)     \u2502             \u2502 (ESTABLISHED)  \u2502<br \/>\n \u2502 request_sock   \u2502             \u2502 \u7b49\u4f60 accept()   \u2502<br \/>\n \u2514\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2518             \u2514\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2518<br \/>\n  \u4e0a\u9650                            \u4e0a\u9650<br \/>\n  tcp_max_syn_backlog        min(backlog, somaxconn)<\/p>\n<p>SYN \u961f\u5217\u653e\u7684\u662f\u534a\u8fde\u63a5&#xff1a;SYN \u6536\u5230\u4e86&#xff0c;SYN&#043;ACK \u53d1\u51fa\u53bb\u4e86&#xff0c;\u7b2c\u4e09\u4e2a\u5305\u8fd8\u6ca1\u56de\u6765\u3002\u4e0a\u9650\u7531\u00a0tcp_max_syn_backlog\u00a0\u63a7\u5236&#xff0c;\u6587\u6863\u8bf4\u660e\u5b83\u662f per-listener \u7684&#xff0c;\u4e14\u4f1a\u968f\u5185\u5b58\u81ea\u52a8\u653e\u5927\u3002\u6ea2\u51fa\u65f6\u82e5\u00a0tcp_syncookies\u00a0\u6253\u5f00&#xff08;\u9ed8\u8ba4\u5c31\u662f 1&#xff09;&#xff0c;\u5185\u6838\u7528 syncookie \u515c\u4f4f&#xff0c;\u628a\u72b6\u6001\u7f16\u7801\u8fdb ISN \u91cc&#xff0c;\u4e0d\u5360\u5185\u5b58\u3002<\/p>\n<p>accept \u961f\u5217\u653e\u7684\u662f\u5df2\u7ecf\u5b8c\u6210\u4e09\u6b21\u63e1\u624b\u3001\u7b49\u7740\u4f60\u00a0accept()\u00a0\u7684\u5168\u8fde\u63a5&#xff0c;\u4e0a\u9650\u662f\u00a0min(listen \u7684 backlog \u53c2\u6570, net.core.somaxconn)\u3002SOMAXCONN\u00a0\u8fd9\u4e2a\u5e38\u91cf\u5728 Linux 5.4 \u91cc\u4ece 128 \u63d0\u5230\u4e86 4096&#xff0c;\u5f88\u591a\u8001\u6846\u67b6\u7684\u9ed8\u8ba4 backlog \u5199\u6b7b\u6210 128&#xff0c;\u5c31\u662f\u90a3\u4e2a\u5e74\u4ee3\u7684\u4ea7\u7269\u3002<\/p>\n<p>accept \u961f\u5217\u6ee1\u4e86\u4f1a\u53d1\u751f\u4ec0\u4e48&#xff0c;\u662f\u8fd9\u4e00\u8282\u6700\u503c\u94b1\u7684\u4e00\u4e2a\u4e8b\u5b9e\u3002\u9ed8\u8ba4\u884c\u4e3a\u662f\u4e22\u5f03\u2014\u2014\u5185\u6838\u628a\u5ba2\u6237\u7aef\u53d1\u6765\u7684\u7b2c\u4e09\u6b21\u63e1\u624b ACK \u76f4\u63a5\u4e22\u6389&#xff0c;\u4ec0\u4e48\u90fd\u4e0d\u56de\u3002\u5ba2\u6237\u7aef\u90a3\u4fa7\u7684\u72b6\u6001\u526f\u672c\u5df2\u7ecf\u662f ESTABLISHED \u4e86&#xff0c;connect()\u00a0\u65e9\u5c31\u8fd4\u56de\u6210\u529f&#xff0c;\u5b83\u5f00\u59cb\u53d1\u6570\u636e&#xff1b;\u670d\u52a1\u7aef\u8fd9\u8fb9\u5185\u6838\u538b\u6839\u6ca1\u5efa\u7acb\u8fd9\u6761\u8fde\u63a5\u3002\u4e09\u4efd\u526f\u672c\u5728\u8fd9\u91cc\u88c2\u6210\u4e86\u4e24\u4e2a\u4e0d\u76f8\u5bb9\u7684\u4e16\u754c&#xff0c;\u800c\u8fd9\u4e2a\u88c2\u7f1d\u662f\u9ed8\u8ba4\u914d\u7f6e\u4e0b\u7684\u6b63\u5e38\u884c\u4e3a&#xff0c;\u65e5\u5fd7\u91cc\u4e00\u4e2a\u5b57\u90fd\u6ca1\u6709\u3002<\/p>\n<p>\u670d\u52a1\u7aef\u4fa7\u552f\u4e00\u7684\u75d5\u8ff9\u662f\u00a0netstat -s\u00a0\u91cc\u7684\u4e24\u4e2a\u8ba1\u6570\u5668&#xff0c;listen queue of a socket overflowed\u00a0\u548c\u00a0SYNs to LISTEN sockets dropped\u3002\u5b83\u4eec\u662f\u6392\u67e5\u300c\u5ba2\u6237\u7aef\u5076\u53d1\u8fde\u63a5\u8d85\u65f6\u800c\u670d\u52a1\u7aef\u6beb\u65e0\u5f02\u5e38\u300d\u7684\u5165\u53e3\u3002<\/p>\n<p>tcp_abort_on_overflow\u00a0\u628a\u884c\u4e3a\u6539\u6210\u56de RST\u3002\u6587\u6863\u5bf9\u5b83\u7684\u6001\u5ea6\u5f88\u660e\u786e&#xff1a;\u300cEnable this option\u00a0only\u00a0if you are really sure that listening daemon cannot be tuned to accept connections faster.\u300d\u9ed8\u8ba4\u5173\u7740\u7684\u7406\u7531\u4e5f\u5199\u4e86\u2014\u2014\u300cif overflow occurred due to a burst, connection will recover\u300d&#xff0c;\u7a81\u53d1\u6d41\u91cf\u4e0b\u4e22\u4e00\u4e2a ACK&#xff0c;\u5ba2\u6237\u7aef\u91cd\u4f20\u5c31\u6062\u590d\u4e86&#xff0c;\u800c RST \u4e0d\u53ef\u6062\u590d\u3002\u8981\u4e0d\u8981\u5f00&#xff0c;\u53d6\u51b3\u4e8e\u4f60\u66f4\u6015\u6162\u8fd8\u662f\u66f4\u6015\u9519&#xff1a;\u5f00\u4e86\u4e4b\u540e\u5ba2\u6237\u7aef\u7acb\u523b\u5931\u8d25\u5e76\u53ef\u4ee5\u91cd\u8bd5\u522b\u7684\u8282\u70b9&#xff0c;\u5173\u7740\u5219\u662f\u8ba9\u5b83\u5728\u8d85\u65f6\u91cc\u8017\u7740\u3002\u6211\u503e\u5411\u4e8e\u5f00&#xff0c;\u524d\u63d0\u662f\u5ba2\u6237\u7aef\u4fa7\u6709\u50cf\u6837\u7684\u91cd\u8bd5\u4e0e\u6458\u9664\u903b\u8f91&#xff1b;\u6ca1\u6709\u7684\u8bdd&#xff0c;\u5f00\u5b83\u53ea\u662f\u628a\u4e00\u79cd\u6545\u969c\u6362\u6210\u53e6\u4e00\u79cd\u3002<\/p>\n<p>\u770b\u961f\u5217\u6df1\u5ea6\u4e0d\u7528\u6293\u5305\u3002ss -lnt\u00a0\u5728 LISTEN \u72b6\u6001\u7684 socket \u4e0a&#xff0c;\u4e24\u4e2a\u5b57\u6bb5\u7684\u8bed\u4e49\u8ddf ESTABLISHED \u65f6\u5b8c\u5168\u4e0d\u540c&#xff1a;<\/p>\n<p>text<\/p>\n<p>$ ss -lnt<br \/>\nState   Recv-Q  Send-Q  Local Address:Port<br \/>\nLISTEN  0       4096          0.0.0.0:8080<br \/>\nLISTEN  129     128           0.0.0.0:9090<\/p>\n<p>Recv-Q\u00a0\u662f\u5f53\u524d accept \u961f\u5217\u91cc\u79ef\u538b\u7684\u8fde\u63a5\u6570&#xff0c;Send-Q\u00a0\u662f\u8fd9\u4e2a\u961f\u5217\u7684\u4e0a\u9650\u3002\u7b2c\u4e8c\u884c\u90a3\u79cd\u00a0Recv-Q\u00a0\u9876\u7740\u00a0Send-Q\u00a0\u7684\u72b6\u6001&#xff0c;\u8bf4\u660e\u5e94\u7528 accept \u7684\u901f\u5ea6\u5df2\u7ecf\u8ddf\u4e0d\u4e0a\u4e86&#xff0c;\u518d\u5f80\u540e\u5c31\u662f\u9759\u9ed8\u4e22\u5f03\u3002\u8fd9\u4e00\u6761\u6211\u653e\u5728\u76d1\u63a7\u91cc&#xff0c;\u6bd4\u770b CPU \u6709\u7528\u5f97\u591a\u3002<\/p>\n<h3>\u534a\u5f00\u8fde\u63a5\u88ab\u53d1\u73b0\u7684\u65f6\u523b&#xff0c;\u662f\u4e00\u4e2a\u53ef\u4ee5\u7b97\u51fa\u6765\u7684\u6570<\/h3>\n<p>\u524d\u9762\u8bf4\u8fc7&#xff0c;\u534a\u5f00\u8fde\u63a5\u9760\u53d1\u6570\u636e\u89e6\u53d1\u6062\u590d\u3002\u8fd9\u53e5\u8bdd\u5bf9\u5199\u670d\u52a1\u7aef\u7684\u4eba\u6765\u8bf4\u4fe1\u606f\u91cf\u4e0d\u591f\u2014\u2014\u771f\u6b63\u8981\u56de\u7b54\u7684\u662f\u591a\u4e45\u3002\u8fd9\u4e2a\u6570\u53ef\u4ee5\u7b97&#xff0c;\u800c\u4e14\u7b97\u51fa\u6765\u7684\u4e09\u4e2a\u91cf\u7ea7\u5dee\u5f97\u5f88\u8fdc&#xff0c;\u6b63\u597d\u5bf9\u5e94\u4e09\u79cd\u6392\u969c\u7ed3\u8bba\u3002<\/p>\n<p>\u7b2c\u4e00\u79cd\u60c5\u51b5&#xff0c;\u5bf9\u7aef\u7684\u673a\u5668\u8fd8\u6d3b\u7740&#xff0c;\u53ea\u662f\u90a3\u6761\u8fde\u63a5\u7684\u72b6\u6001\u6ca1\u4e86&#xff1a;\u8fdb\u7a0b\u91cd\u542f\u3001\u5bb9\u5668\u6362\u4ee3\u3001\u534f\u8bae\u6808\u91cd\u7f6e\u3002\u4f60\u53d1\u8fc7\u53bb\u4e00\u4e2a\u5e26\u6570\u636e\u7684\u5305&#xff0c;\u5bf9\u7aef\u5185\u6838\u5728\u81ea\u5df1\u7684\u8fde\u63a5\u8868\u91cc\u67e5\u4e0d\u5230\u8fd9\u4e2a\u56db\u5143\u7ec4&#xff0c;\u6309\u6807\u51c6\u56de\u4e00\u4e2a RST\u3002\u4f60\u7684\u4e0b\u4e00\u6b21\u00a0read\u00a0\u6216\u00a0write\u00a0\u7acb\u523b\u62ff\u5230\u00a0ECONNRESET\u3002\u5ef6\u8fdf\u7b49\u4e8e\u4e00\u4e2a RTT\u3002\u00a0\u8fd9\u662f\u6700\u5e78\u8fd0\u7684\u60c5\u51b5&#xff0c;\u4e5f\u662f\u6700\u5e38\u89c1\u7684\u3002<\/p>\n<p>\u7b2c\u4e8c\u79cd\u60c5\u51b5&#xff0c;\u5bf9\u7aef\u6574\u53f0\u673a\u5668\u6389\u7ebf&#xff0c;\u6216\u8005\u4e2d\u95f4\u6709\u8bbe\u5907\u628a\u5305\u9759\u9ed8\u4e22\u6389\u3002\u9632\u706b\u5899\u8001\u5316\u6389\u4e86\u4f1a\u8bdd\u8868\u662f\u5178\u578b\u6210\u56e0&#xff0c;\u5f88\u591a\u8bbe\u5907\u7684 TCP \u4f1a\u8bdd\u9ed8\u8ba4\u8001\u5316\u65f6\u95f4\u662f\u4e09\u5230\u4e94\u5206\u949f&#xff0c;\u4e14\u8fc7\u671f\u540e\u4e0d\u53d1 RST\u3002\u4f60\u7684\u5305\u53d1\u51fa\u53bb&#xff0c;\u6ca1\u6709\u4efb\u4f55\u56de\u5e94\u3002\u5185\u6838\u5f00\u59cb\u91cd\u4f20&#xff0c;\u6309\u6307\u6570\u9000\u907f&#xff0c;\u76f4\u5230\u00a0tcp_retries2\u00a0\u7528\u5b8c\u3002\u6587\u6863\u628a\u8fd9\u4e2a\u6570\u7b97\u597d\u4e86&#xff1a;<\/p>\n<p>This value influences the timeout of an alive TCP connection, when RTO retransmissions remain unacknowledged. Given a value of N, a hypothetical TCP connection following exponential backoff with an initial RTO of TCP_RTO_MIN would retransmit N times before killing the connection at the (N&#043;1)th RTO.\u00a0The default value of 15 yields a hypothetical timeout of 924.6 seconds\u00a0and is a lower bound for the effective timeout.<\/p>\n<p>\u4e5d\u767e\u4e8c\u5341\u56db\u70b9\u516d\u79d2&#xff0c;\u7ea6\u5341\u4e94\u5206\u534a&#xff0c;\u800c\u4e14\u6587\u6863\u5f3a\u8c03\u8fd9\u662f\u4e0b\u754c\u3002\u8fd9\u5c31\u662f\u90a3\u79cd\u300c\u670d\u52a1\u7aef\u8bf4\u8fde\u63a5\u8fd8\u5728&#xff0c;\u5ba2\u6237\u7aef\u65e9\u5c31\u8d70\u4e86&#xff0c;\u5341\u4e94\u5206\u949f\u540e\u7a81\u7136\u4e00\u6279\u9519\u8bef\u300d\u7684\u6210\u56e0\u3002\u8fd9\u4e2a\u6570\u53ef\u4ee5\u901a\u8fc7\u00a0TCP_USER_TIMEOUT\u00a0\u8fd9\u4e2a socket \u9009\u9879\u76f4\u63a5\u538b\u5230\u4f60\u60f3\u8981\u7684\u6beb\u79d2\u6570&#xff0c;\u5b83\u6bd4\u8c03\u5168\u5c40\u00a0tcp_retries2\u00a0\u7cbe\u786e\u5f97\u591a&#xff0c;\u56e0\u4e3a\u5b83\u662f per-socket \u7684\u3002\u5199\u957f\u8fde\u63a5\u4e2d\u95f4\u4ef6\u7684\u8bdd&#xff0c;\u8fd9\u4e2a\u9009\u9879\u6bd4 keepalive \u66f4\u8be5\u5148\u8bbe\u3002<\/p>\n<p>\u7b2c\u4e09\u79cd\u60c5\u51b5&#xff0c;\u4f60\u4ec0\u4e48\u90fd\u4e0d\u53d1\u3002\u94fe\u8def\u7a7a\u95f2&#xff0c;\u4e24\u7aef\u5404\u81ea\u8eba\u7740\u3002\u8fd9\u65f6\u5019\u552f\u4e00\u7684\u53d1\u73b0\u673a\u5236\u662f\u00a0SO_KEEPALIVE&#xff0c;\u800c\u5b83\u7684\u9ed8\u8ba4\u65f6\u95f4\u53c2\u6570\u662f\u8fd9\u6837\u7684&#xff1a;<\/p>\n<p>C<\/p>\n<p>\/* include\/net\/tcp.h, Linux 6.6 *\/<br \/>\n#define TCP_KEEPALIVE_TIME   (120*60*HZ) \/* two hours *\/<br \/>\n#define TCP_KEEPALIVE_PROBES 9           \/* Max of 9 keepalive probes *\/<br \/>\n#define TCP_KEEPALIVE_INTVL  (75*HZ)<\/p>\n<p>\u4e24\u5c0f\u65f6\u7a7a\u95f2\u4e4b\u540e\u624d\u53d1\u7b2c\u4e00\u4e2a\u63a2\u6d4b\u5305&#xff0c;\u7136\u540e\u6bcf\u4e03\u5341\u4e94\u79d2\u4e00\u6b21&#xff0c;\u4e5d\u6b21\u90fd\u6ca1\u56de\u5e94\u624d\u5224\u6b7b\u3002\u52a0\u8d77\u6765\u662f 7200 \u52a0 675&#xff0c;\u7b49\u4e8e 7875 \u79d2&#xff0c;\u4e24\u5c0f\u65f6\u5341\u4e00\u5206\u949f\u5341\u4e94\u79d2\u3002<\/p>\n<p>\u6211\u5f53\u65f6\u7ed9\u90a3\u6279\u8fde\u63a5\u5f00\u4e86\u00a0SO_KEEPALIVE&#xff0c;\u7b2c\u4e8c\u5929\u770b\u5230\u786e\u5b9e\u6e05\u6389\u4e86\u4e00\u6279&#xff0c;\u5c31\u628a\u5b83\u8bb0\u6210\u4e86\u4e00\u6761\u6709\u6548\u63aa\u65bd\u3002\u56de\u8fc7\u5934\u770b&#xff0c;\u90a3\u662f\u6211\u7b2c\u4e8c\u4e2a\u5224\u65ad\u9519\u8bef&#xff1a;\u6e05\u6389\u7684\u65f6\u95f4\u70b9\u96c6\u4e2d\u5728\u4e24\u5c0f\u65f6\u4e4b\u540e&#xff0c;\u8bf4\u660e\u751f\u6548\u7684\u662f\u8fd9\u6761\u9ed8\u8ba4\u8def\u5f84&#xff0c;\u800c\u6545\u969c\u8fde\u63a5\u7684\u4ea7\u751f\u901f\u7387\u8fdc\u9ad8\u4e8e\u6bcf\u4e24\u5c0f\u65f6\u6e05\u4e00\u6b21\u7684\u901f\u5ea6\u3002\u4e00\u4e2a\u628a\u6e05\u7406\u5468\u671f\u8bbe\u6210\u4e24\u5c0f\u65f6\u7684\u673a\u5236&#xff0c;\u53bb\u6cbb\u4e00\u4e2a\u6bcf\u5206\u949f\u90fd\u5728\u4ea7\u751f\u65b0\u5b9e\u4f8b\u7684\u73b0\u8c61&#xff0c;\u770b\u4e0a\u53bb\u6709\u6548\u53ea\u662f\u56e0\u4e3a\u89c2\u5bdf\u7a97\u53e3\u591f\u957f\u3002\u00a0\u75c7\u72b6\u56db\u5f52\u4f4d\u3002<\/p>\n<p>\u4e09\u4e2a\u6570\u653e\u5728\u4e00\u8d77&#xff0c;\u7ed3\u8bba\u5c31\u51fa\u6765\u4e86&#xff1a;<\/p>\n<table>\n<tbody>\n<tr>\n<p>\u89e6\u53d1\u6761\u4ef6<\/p>\n<p>\u53d1\u73b0\u5ef6\u8fdf<\/p>\n<p>\u51b3\u5b9a\u5b83\u7684\u53c2\u6570<\/p>\n<\/tr>\n<tr>\n<td>\n<p>\u53d1\u6570\u636e&#xff0c;\u5bf9\u7aef\u5728\u7ebf<\/p>\n<\/td>\n<td>\n<p>\u4e00\u4e2a RTT<\/p>\n<\/td>\n<td>\n<p>\u65e0<\/p>\n<\/td>\n<\/tr>\n<tr>\n<td>\n<p>\u53d1\u6570\u636e&#xff0c;\u5bf9\u7aef\u4e0d\u53ef\u8fbe<\/p>\n<\/td>\n<td>\n<p>\u2265 924.6 \u79d2<\/p>\n<\/td>\n<td>\n<p>tcp_retries2\u00a0\/\u00a0TCP_USER_TIMEOUT<\/p>\n<\/td>\n<\/tr>\n<tr>\n<td>\n<p>\u7a7a\u95f2&#xff0c;\u5f00\u4e86 keepalive<\/p>\n<\/td>\n<td>\n<p>7875 \u79d2<\/p>\n<\/td>\n<td>\n<p>\u4e09\u4e2a\u00a0tcp_keepalive_*<\/p>\n<\/td>\n<\/tr>\n<tr>\n<td>\n<p>\u7a7a\u95f2&#xff0c;\u672a\u5f00 keepalive<\/p>\n<\/td>\n<td>\n<p>\u6c38\u4e0d<\/p>\n<\/td>\n<td>\n<p>\u65e0<\/p>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p>\u5185\u6838\u7ed9\u7684\u9ed8\u8ba4\u503c\u5168\u90fd\u662f\u4e3a\u957f\u8fde\u63a5\u7684\u5b58\u6d3b\u4f18\u5316\u7684&#xff0c;\u800c\u5206\u5e03\u5f0f\u7cfb\u7edf\u8981\u7684\u662f\u53ca\u65f6\u53d1\u73b0\u6b7b\u4ea1&#xff0c;\u4e24\u8005\u7684\u65b9\u5411\u76f8\u53cd\u3002\u6240\u4ee5\u751f\u4ea7\u4e0a\u771f\u6b63\u9760\u5f97\u4f4f\u7684\u662f\u5e94\u7528\u5c42\u5fc3\u8df3&#xff1a;\u5468\u671f\u53ef\u4ee5\u8bbe\u6210\u79d2\u7ea7&#xff0c;\u800c\u4e14\u5b83\u63a2\u6d4b\u7684\u662f\u5e94\u7528\u662f\u5426\u8fd8\u80fd\u5904\u7406\u8bf7\u6c42&#xff0c;\u5185\u6838 keepalive \u53ea\u80fd\u63a2\u6d4b\u534f\u8bae\u6808\u662f\u5426\u8fd8\u5728\u5e94\u7b54\u3002\u4e00\u4e2a GC \u505c\u987f\u4e09\u5341\u79d2\u7684\u8fdb\u7a0b&#xff0c;\u5185\u6838 keepalive \u5168\u7a0b\u6b63\u5e38\u3002<\/p>\n<h3>write \u8fd4\u56de\u6210\u529f&#xff0c;\u53ea\u8bc1\u660e\u6570\u636e\u8fdb\u4e86\u672c\u673a\u7684\u53d1\u9001\u961f\u5217<\/h3>\n<p>\u628a TCP \u53ef\u9760\u6027\u7684\u8fb9\u754c\u4e00\u6b21\u8bf4\u6e05\u695a&#xff1a;\u5b83\u4fdd\u8bc1\u7684\u662f\u5b57\u8282\u6d41\u6309\u5e8f\u3001\u5b8c\u6574\u3001\u4e0d\u91cd\u590d\u5730\u4ea4\u4ed8\u5230\u5bf9\u7aef\u5185\u6838\u7684\u63a5\u6536\u961f\u5217&#xff0c;\u6b62\u6b65\u4e8e\u6b64\u3002\u00a0\u5bf9\u7aef\u7684\u5e94\u7528\u6709\u6ca1\u6709\u00a0read\u3001\u8bfb\u4e86\u6709\u6ca1\u6709\u5904\u7406\u6210\u529f\u3001\u5904\u7406\u5b8c\u6709\u6ca1\u6709\u843d\u5e93&#xff0c;TCP \u4e00\u65e0\u6240\u77e5&#xff0c;\u4e5f\u6ca1\u6709\u4efb\u4f55\u5b57\u6bb5\u80fd\u8868\u8fbe\u8fd9\u4e9b\u3002<\/p>\n<p>\u8fd9\u6761\u8fb9\u754c\u6b63\u662f\u4e09\u526f\u672c\u6a21\u578b\u7684\u76f4\u63a5\u540e\u679c\u3002TCP \u662f\u672c\u7aef\u5185\u6838\u4e0e\u5bf9\u7aef\u5185\u6838\u4e4b\u95f4\u7684\u540c\u6b65\u534f\u8bae&#xff0c;\u5b83\u540c\u6b65\u7684\u662f\u524d\u4e24\u4efd\u526f\u672c\u3002\u7b2c\u4e09\u4efd\u526f\u672c\u2014\u2014\u5bf9\u7aef\u7684\u8fdb\u7a0b\u2014\u2014\u4e0d\u5728\u5b83\u7684\u7ba1\u8f96\u8303\u56f4\u91cc\u3002<\/p>\n<p>\u6240\u4ee5\u00a0write()\u00a0\u8fd4\u56de\u4e00\u4e2a\u6b63\u6570&#xff0c;\u542b\u4e49\u53ea\u6709\u4e00\u4e2a&#xff1a;\u8fd9\u4e48\u591a\u5b57\u8282\u5df2\u7ecf\u4ece\u4f60\u7684\u7528\u6237\u6001\u7f13\u51b2\u533a\u62f7\u8fdb\u4e86\u5185\u6838\u7684\u53d1\u9001\u961f\u5217\u3002\u6b64\u523b\u5b83\u53ef\u80fd\u8fd8\u6ca1\u4e0a\u7f51\u7ebf\u3002<\/p>\n<p>\u6211\u5728\u4e00\u4e2a\u6d88\u606f\u7f51\u5173\u4e0a\u6309\u300cwrite \u6210\u529f\u5373\u6295\u9012\u6210\u529f\u300d\u8bb0\u8fc7\u6295\u9012\u72b6\u6001&#xff0c;\u8dd1\u4e86\u534a\u5e74\u6ca1\u4e8b&#xff0c;\u4e00\u6b21\u673a\u623f\u4fa7\u7684\u4ea4\u6362\u673a\u6545\u969c\u671f\u95f4\u96c6\u4e2d\u66b4\u9732&#xff1a;\u90a3\u534a\u5206\u949f\u91cc\u00a0write()\u00a0\u5168\u90e8\u6210\u529f\u8fd4\u56de&#xff0c;\u6570\u636e\u5168\u5728\u00a0sk_wmem\u00a0\u91cc\u6392\u961f&#xff0c;\u8fde\u63a5\u968f\u540e\u88ab\u00a0tcp_retries2\u00a0\u5224\u6b7b&#xff0c;\u51e0\u4e07\u6761\u6d88\u606f\u7684\u72b6\u6001\u662f\u300c\u5df2\u6295\u9012\u300d\u800c\u5bf9\u7aef\u4e00\u6761\u90fd\u6ca1\u6536\u5230\u3002\u8865\u6551\u9760\u7684\u662f\u4e0b\u6e38\u5bf9\u8d26&#xff0c;\u4ee3\u4ef7\u662f\u4e24\u5929\u3002\u8fd9\u4e2a\u9519\u8bef\u7684\u5f62\u72b6\u5f88\u5178\u578b&#xff1a;\u628a\u672c\u673a\u7684\u4e00\u6b21\u5185\u5b58\u62f7\u8d1d&#xff0c;\u5f53\u6210\u4e86\u8de8\u673a\u7684\u4e00\u6b21\u72b6\u6001\u540c\u6b65\u3002<\/p>\n<p>\u53cd\u8fc7\u6765\u770b&#xff0c;\u4e3a\u4e86\u505a\u5230\u300c\u6309\u5e8f\u5b8c\u6574\u4ea4\u4ed8\u5230\u5bf9\u7aef\u5185\u6838\u300d&#xff0c;TCP \u624b\u91cc\u7684\u673a\u5236\u6709\u4e94\u4ef6&#xff0c;\u5b83\u4eec\u5404\u81ea\u89e3\u51b3\u540c\u6b65\u94fe\u8def\u4e0a\u7684\u4e00\u79cd\u5931\u8d25&#xff1a;<\/p>\n<p>\u5e8f\u53f7\u4e0e\u7d2f\u79ef\u786e\u8ba4\u662f\u57fa\u7840\u3002\u6bcf\u4e2a\u5b57\u8282\u6709\u4e00\u4e2a\u5e8f\u53f7&#xff0c;ACK \u53f7\u7684\u8bed\u4e49\u662f\u300c\u8fd9\u4e2a\u5e8f\u53f7\u4e4b\u524d\u7684\u5b57\u8282\u6211\u5168\u6536\u5230\u4e86\u300d\u3002\u7d2f\u79ef\u786e\u8ba4\u7684\u597d\u5904\u662f ACK \u4e22\u4e00\u4e2a\u4e0d\u8981\u7d27&#xff0c;\u540e\u4e00\u4e2a ACK \u8986\u76d6\u524d\u4e00\u4e2a&#xff1b;\u4ee3\u4ef7\u662f\u5b83\u8868\u8fbe\u4e0d\u4e86\u300c\u6211\u6536\u5230\u4e86 1-1000 \u548c 2001-3000&#xff0c;\u7f3a 1001-2000\u300d\u8fd9\u79cd\u7a7a\u6d1e\u3002SACK \u9009\u9879\u8865\u7684\u5c31\u662f\u8fd9\u4e2a\u6d1e&#xff0c;\u5b83\u8ba9\u53d1\u9001\u65b9\u53ea\u91cd\u4f20\u771f\u6b63\u7f3a\u7684\u90a3\u6bb5&#xff0c;\u800c\u4e0d\u662f\u4ece\u7a7a\u6d1e\u5904\u5168\u90e8\u91cd\u6765\u3002\u6ca1\u6709 SACK \u7684\u5e74\u4ee3&#xff0c;\u4e00\u4e2a\u4e22\u5305\u4f1a\u8ba9\u540e\u9762\u6240\u6709\u5df2\u7ecf\u5b89\u5168\u5230\u8fbe\u7684\u6570\u636e\u767d\u8dd1\u4e00\u8d9f\u3002<\/p>\n<p>\u8d85\u65f6\u91cd\u4f20\u5904\u7406\u7684\u662f ACK \u4e00\u76f4\u4e0d\u6765\u3002RTO \u7531 RTT \u7684\u6ed1\u52a8\u4f30\u8ba1\u63a8\u51fa\u6765&#xff0c;\u5185\u6838\u7ef4\u62a4 SRTT \u548c RTTVAR \u4e24\u4e2a\u91cf&#xff0c;\u91cd\u4f20\u65f6\u6309\u6307\u6570\u9000\u907f&#xff0c;\u9000\u5230\u00a0tcp_retries2\u00a0\u7528\u5b8c\u4e3a\u6b62\u2014\u2014\u4e0a\u4e00\u8282\u90a3\u4e2a 924.6 \u79d2\u5c31\u662f\u4ece\u8fd9\u91cc\u6765\u7684\u3002\u8fd9\u91cc\u6709\u4e2a\u5bb9\u6613\u5ffd\u7565\u7684\u7ec6\u8282&#xff1a;\u91cd\u4f20\u62a5\u6587\u7684 RTT \u91c7\u6837\u662f\u4e0d\u53ef\u4fe1\u7684&#xff08;\u6536\u5230\u7684 ACK \u5bf9\u5e94\u7684\u662f\u539f\u5305\u8fd8\u662f\u91cd\u4f20\u5305\u5206\u4e0d\u6e05&#xff09;&#xff0c;\u6240\u4ee5\u5185\u6838\u6309 Karn \u7b97\u6cd5\u8df3\u8fc7\u91cd\u4f20\u6837\u672c&#xff0c;\u53ea\u7528\u9000\u907f\u540e\u7684 RTO\u3002<\/p>\n<p>\u5feb\u901f\u91cd\u4f20\u5904\u7406\u7684\u662f\u300c\u53ea\u4e22\u4e86\u4e00\u4e2a\u5305&#xff0c;\u4f46\u540e\u9762\u7684\u90fd\u5230\u4e86\u300d\u3002\u63a5\u6536\u65b9\u6bcf\u6536\u5230\u4e00\u4e2a\u5931\u5e8f\u6bb5\u5c31\u7acb\u523b\u56de\u4e00\u4e2a\u91cd\u590d ACK&#xff0c;\u53d1\u9001\u65b9\u6570\u5230\u4e09\u4e2a\u91cd\u590d ACK \u5c31\u4e0d\u7b49 RTO \u76f4\u63a5\u91cd\u4f20\u3002\u4e09\u8fd9\u4e2a\u6570\u5b57\u662f\u4e3a\u4e86\u533a\u5206\u300c\u4e71\u5e8f\u300d\u548c\u300c\u771f\u4e22\u300d\u2014\u2014\u7f51\u7edc\u5185\u7684\u8f7b\u5ea6\u4e71\u5e8f\u901a\u5e38\u4ea7\u751f\u4e00\u5230\u4e24\u4e2a\u91cd\u590d ACK\u3002<\/p>\n<p>\u6ed1\u52a8\u7a97\u53e3\u662f\u63a5\u6536\u65b9\u5bf9\u53d1\u9001\u65b9\u7684\u6d41\u91cf\u63a7\u5236\u3002\u63a5\u6536\u65b9\u5728\u6bcf\u4e2a ACK \u91cc\u5e26\u4e0a\u81ea\u5df1\u8fd8\u80fd\u6536\u591a\u5c11&#xff08;rwnd&#xff09;&#xff0c;\u53d1\u9001\u65b9\u53d1\u51fa\u53bb\u4f46\u672a\u88ab\u786e\u8ba4\u7684\u6570\u636e\u4e0d\u80fd\u8d85\u8fc7\u5b83\u3002\u7a97\u53e3\u5b57\u6bb5\u53ea\u6709 16 \u4f4d&#xff0c;\u4e0a\u9650 64KB&#xff0c;\u73b0\u4ee3\u94fe\u8def\u8fdc\u8fdc\u4e0d\u591f&#xff0c;\u9760 SYN \u91cc\u7684\u7a97\u53e3\u7f29\u653e\u9009\u9879\u628a\u5b83\u5de6\u79fb\u6700\u591a 14 \u4f4d\u3002\u7f29\u653e\u56e0\u5b50\u53ea\u5728\u63e1\u624b\u65f6\u534f\u5546\u4e00\u6b21&#xff0c;\u8fd9\u662f\u53c8\u4e00\u5904\u300c\u53ea\u8bf4\u4e00\u904d\u7684\u72b6\u6001\u300d\u2014\u2014\u4e2d\u95f4\u8bbe\u5907\u5982\u679c\u5265\u6389\u4e86 SYN \u91cc\u7684\u7a97\u53e3\u7f29\u653e\u9009\u9879&#xff0c;\u4e24\u7aef\u5bf9\u7a97\u53e3\u5927\u5c0f\u7684\u7406\u89e3\u4f1a\u5dee\u51e0\u4e2a\u6570\u91cf\u7ea7&#xff0c;\u8868\u73b0\u662f\u541e\u5410\u8be1\u5f02\u5730\u5361\u5728\u67d0\u4e2a\u4f4e\u503c\u4e0a\u3002<\/p>\n<p>rwnd \u7684\u5b9e\u9645\u6765\u6e90\u662f\u63a5\u6536\u7f13\u51b2\u533a\u7684\u5269\u4f59\u7a7a\u95f4&#xff0c;\u800c\u7f13\u51b2\u533a\u5927\u5c0f\u7531\u00a0tcp_rmem\u00a0\u81ea\u52a8\u8c03\u8282&#xff1a;<\/p>\n<p>tcp_rmem \u2014 min: Default: 4K. default: initial size of receive buffer used by TCP sockets. Default: 131072 bytes. max: Default: between 131072 and 6MB, depending on RAM size.<\/p>\n<p>\u4e8e\u662f\u6709\u4e00\u6761\u76f4\u63a5\u7684\u56e0\u679c\u94fe&#xff1a;\u4f60\u7684\u5e94\u7528\u8bfb\u5f97\u6162&#xff0c;\u63a5\u6536\u7f13\u51b2\u533a\u88ab\u5360\u6ee1&#xff0c;rwnd \u7f29\u5c0f&#xff0c;\u5bf9\u7aef\u7684\u53d1\u9001\u7a97\u53e3\u88ab\u538b\u4f4f&#xff0c;\u6700\u7ec8\u5bf9\u7aef\u7684\u00a0write()\u00a0\u963b\u585e\u6216\u8fd4\u56de EAGAIN\u3002\u80cc\u538b\u662f\u4ece\u4f60\u7684\u00a0read\u00a0\u8c03\u7528\u4e00\u8def\u4f20\u56de\u5bf9\u7aef\u5e94\u7528\u7684&#xff0c;\u4e2d\u95f4\u7ecf\u8fc7\u56db\u6b21\u8f6c\u6362&#xff0c;\u6bcf\u6b21\u8f6c\u6362\u90fd\u6709\u5ef6\u8fdf\u3002\u8fd9\u4e5f\u662f\u4e3a\u4ec0\u4e48\u6162\u6d88\u8d39\u8005\u4f1a\u62d6\u57ae\u4e0a\u6e38&#xff0c;\u800c\u76d1\u63a7\u4e0a\u770b\u4e24\u7aef\u7684 CPU \u90fd\u4e0d\u9ad8\u3002<\/p>\n<p>rwnd \u964d\u5230\u96f6\u65f6&#xff0c;\u53d1\u9001\u65b9\u8fdb\u5165\u96f6\u7a97\u53e3\u63a2\u6d4b&#xff1a;\u5b9a\u671f\u53d1\u4e00\u4e2a\u5b57\u8282\u7684\u63a2\u6d4b\u5305\u95ee\u300c\u73b0\u5728\u80fd\u6536\u4e86\u5417\u300d\u3002\u8fd9\u4e2a\u673a\u5236\u662f\u5fc5\u987b\u7684&#xff0c;\u56e0\u4e3a\u300c\u7a97\u53e3\u5f00\u4e86\u300d\u8fd9\u6761\u6d88\u606f\u672c\u8eab\u5982\u679c\u4e22\u4e86&#xff0c;\u53cc\u65b9\u4f1a\u6c38\u4e45\u7b49\u5f85\u2014\u2014\u4e00\u4e2a\u53ea\u9760\u5bf9\u7aef\u4e3b\u52a8\u901a\u77e5\u7684\u8bbe\u8ba1&#xff0c;\u5728\u4e22\u5305\u9762\u524d\u4e00\u5b9a\u4f1a\u6b7b\u9501\u3002<\/p>\n<p>\u62e5\u585e\u63a7\u5236\u662f\u5bf9\u7f51\u7edc\u7684\u4f30\u8ba1&#xff0c;\u8ddf\u63a5\u6536\u65b9\u65e0\u5173\u3002cwnd \u548c rwnd \u53d6\u6700\u5c0f\u503c\u51b3\u5b9a\u5b9e\u9645\u53d1\u9001\u91cf\u3002\u6162\u542f\u52a8\u3001\u62e5\u585e\u907f\u514d\u3001\u5feb\u6062\u590d\u8fd9\u5957\u662f Reno \u7cfb\u7684\u9aa8\u67b6&#xff0c;Linux \u9ed8\u8ba4\u7528 CUBIC&#xff0c;\u628a\u7a97\u53e3\u589e\u957f\u5199\u6210\u5173\u4e8e\u300c\u8ddd\u79bb\u4e0a\u6b21\u4e22\u5305\u7684\u65f6\u95f4\u300d\u7684\u4e09\u6b21\u51fd\u6570&#xff0c;\u5728\u9ad8\u5e26\u5bbd\u957f\u5ef6\u8fdf\u94fe\u8def\u4e0a\u6bd4 Reno \u6fc0\u8fdb\u5f97\u591a\u3002BBR \u6362\u4e86\u4e00\u6761\u8def&#xff0c;\u7528\u5e26\u5bbd\u548c RTT \u7684\u4e58\u79ef\u4f30\u8ba1\u7ba1\u9053\u5bb9\u91cf&#xff0c;\u4e0d\u518d\u628a\u4e22\u5305\u5f53\u6210\u62e5\u585e\u4fe1\u53f7\u2014\u2014\u5728\u6709\u968f\u673a\u4e22\u5305\u7684\u65e0\u7ebf\u6216\u8de8\u6d0b\u94fe\u8def\u4e0a\u8fd9\u4e2a\u5dee\u522b\u5f88\u5927\u3002\u5207\u6362\u7528\u00a0net.ipv4.tcp_congestion_control&#xff0c;\u662f\u5c11\u6570\u51e0\u4e2a\u6539\u4e86\u7acb\u523b\u80fd\u91cf\u5230\u6548\u679c\u7684\u53c2\u6570\u3002<\/p>\n<p>\u6821\u9a8c\u548c\u5904\u7406\u7684\u662f\u94fe\u8def\u4e0a\u7684\u4f4d\u7ffb\u8f6c\u3002TCP \u6821\u9a8c\u548c\u662f 16 \u4f4d\u53cd\u7801\u6c42\u548c&#xff0c;\u5f3a\u5ea6\u5f88\u5f31&#xff0c;\u4e00\u4e2a 16 \u4f4d\u5b57\u91cc\u7ffb\u4e24\u4f4d\u5c31\u53ef\u80fd\u6821\u9a8c\u901a\u8fc7\u3002\u73b0\u4ee3\u7f51\u5361\u628a\u5b83\u5378\u8f7d\u5230\u786c\u4ef6&#xff0c;ethtool -k\u00a0\u91cc\u7684\u00a0rx-checksumming\u00a0\u5c31\u662f\u5b83\u3002\u6570\u636e\u5b8c\u6574\u6027\u771f\u8981\u4fdd\u8bc1&#xff0c;\u5e94\u7528\u5c42\u8fd8\u5f97\u81ea\u5df1\u6709\u4e00\u5c42&#xff0c;\u5c24\u5176\u662f\u8de8\u516c\u7f51\u957f\u65f6\u95f4\u4f20\u5927\u6587\u4ef6\u7684\u573a\u666f\u3002<\/p>\n<p>\u4e94\u4ef6\u4e8b\u51d1\u5728\u4e00\u8d77&#xff0c;\u5f97\u5230\u7684\u4ecd\u7136\u53ea\u662f\u300c\u5bf9\u7aef\u5185\u6838\u6536\u5230\u4e86\u300d\u3002\u8de8\u8d8a\u7b2c\u4e09\u4efd\u526f\u672c\u7684\u786e\u8ba4&#xff0c;\u53ea\u80fd\u7531\u5e94\u7528\u5c42\u81ea\u5df1\u53d1&#xff0c;\u8fd9\u5c31\u662f\u6240\u6709 RPC \u6846\u67b6\u90fd\u8981\u6709\u81ea\u5df1\u7684\u54cd\u5e94\u62a5\u6587\u3001\u6240\u6709\u6d88\u606f\u961f\u5217\u90fd\u8981\u6709\u4e1a\u52a1 ack \u7684\u539f\u56e0\u3002\u5b83\u8ddf TCP \u53ef\u9760\u4e0d\u53ef\u9760\u6ca1\u5173\u7cfb&#xff0c;\u5b83\u662f\u53ef\u9760\u6027\u8fb9\u754c\u7684\u4f4d\u7f6e\u51b3\u5b9a\u7684\u3002<\/p>\n<h3>MSS \u662f\u63e1\u624b\u65f6\u8bf4\u7684\u4e00\u53e5\u8bdd&#xff0c;MTU \u662f\u8def\u4e0a\u6bcf\u4e00\u8df3\u7684\u73b0\u5b9e<\/h3>\n<p>\u6709\u4e00\u7c7b\u6545\u969c\u7684\u5f62\u72b6\u6781\u5176\u56fa\u5b9a&#xff1a;\u8fde\u63a5\u80fd\u5efa\u7acb&#xff0c;\u5c0f\u5305\u4e00\u5207\u6b63\u5e38&#xff0c;\u5927\u5305\u4e00\u53d1\u5c31\u5361\u6b7b\u3002SSH \u80fd\u767b\u5f55\u3001\u80fd\u6572\u547d\u4ee4\u3001\u80fd\u770b\u5230\u63d0\u793a\u7b26&#xff0c;ls\u00a0\u4e00\u4e2a\u5927\u76ee\u5f55\u5c31\u518d\u4e5f\u6ca1\u6709\u56de\u97f3\u3002HTTP \u7684 GET \u6b63\u5e38&#xff0c;POST \u4e00\u4e2a\u51e0 KB \u7684 body \u5c31\u8d85\u65f6\u3002<\/p>\n<p>\u8fd9\u7c7b\u6545\u969c\u7684\u6839\u56e0\u51e0\u4e4e\u603b\u662f\u540c\u4e00\u4e2a&#xff0c;\u800c\u5b83\u6b63\u597d\u662f\u4e09\u526f\u672c\u6a21\u578b\u5728\u8def\u5f84\u8fd9\u4e2a\u7ef4\u5ea6\u4e0a\u7684\u6295\u5f71&#xff1a;\u4e24\u7aef\u5bf9\u300c\u4e00\u4e2a\u5305\u6700\u5927\u80fd\u6709\u591a\u5927\u300d\u7684\u5047\u8bbe&#xff0c;\u8ddf\u8def\u5f84\u4e0a\u67d0\u4e00\u8df3\u7684\u73b0\u5b9e\u5bf9\u4e0d\u4e0a\u3002<\/p>\n<p>\u5148\u628a\u4e24\u4e2a\u91cf\u7684\u5173\u7cfb\u6446\u6e05\u695a\u3002MTU \u662f\u94fe\u8def\u5c42\u4e00\u5e27\u80fd\u88c5\u7684\u8f7d\u8377\u4e0a\u9650&#xff0c;\u4ee5\u592a\u7f51\u9ed8\u8ba4 1500 \u5b57\u8282\u3002MSS \u662f TCP \u6bb5\u91cc\u6570\u636e\u90e8\u5206\u7684\u4e0a\u9650&#xff0c;\u7b49\u4e8e MTU \u51cf\u53bb IP \u5934\u548c TCP \u5934&#xff0c;\u65e0\u9009\u9879\u7684 IPv4 \u662f 1500 \u51cf 40 \u7b49\u4e8e 1460\u3002<\/p>\n<p>\u5173\u952e\u5728\u4e8e\u5b83\u4eec\u7684\u540c\u6b65\u65b9\u5f0f\u5b8c\u5168\u4e0d\u540c\u3002MSS \u5728 SYN \u548c SYN&#043;ACK \u91cc\u5404\u5ba3\u544a\u4e00\u6b21&#xff0c;\u6b64\u540e\u518d\u4e5f\u4e0d\u91cd\u8bf4&#xff1b;\u800c\u4e14\u5b83\u7684\u8bed\u4e49\u662f\u300c\u6211\u80fd\u6536\u591a\u5927\u300d&#xff0c;\u4e0d\u662f\u300c\u6211\u8981\u53d1\u591a\u5927\u300d\u3002\u53cc\u65b9\u5404\u81ea\u5ba3\u544a&#xff0c;\u5404\u81ea\u8bb0\u4e0b\u5bf9\u7aef\u7684\u503c&#xff0c;\u53d1\u9001\u65f6\u53d6\u81ea\u5df1\u90a3\u6761\u8def\u5f84\u4e0a\u7684\u4f30\u8ba1\u4e0e\u5bf9\u7aef\u5ba3\u544a\u503c\u7684\u8f83\u5c0f\u8005\u3002<\/p>\n<p>MTU \u5462&#xff0c;\u8def\u5f84\u4e0a\u6bcf\u4e00\u8df3\u90fd\u6709\u81ea\u5df1\u7684\u503c&#xff0c;\u4e2d\u95f4\u4efb\u4f55\u4e00\u8df3\u90fd\u53ef\u80fd\u6bd4\u4e24\u7aef\u5c0f&#xff0c;\u800c\u4e24\u7aef\u5728\u63e1\u624b\u65f6\u5bf9\u6b64\u4e00\u65e0\u6240\u77e5\u3002\u96a7\u9053\u662f\u6700\u5e38\u89c1\u7684\u6210\u56e0&#xff1a;VXLAN \u5c01\u88c5\u5403\u6389 50 \u5b57\u8282&#xff0c;\u628a 1500 \u7684\u5e95\u5c42 MTU \u538b\u6210 1450&#xff1b;PPPoE \u662f 1492&#xff1b;IPsec \u89c6\u7b97\u6cd5\u5728 1400 \u4e0a\u4e0b\u3002\u5bb9\u5668\u7f51\u7edc\u91cc\u8fd9\u51e0\u4e4e\u662f\u5e38\u6001\u3002<\/p>\n<p>\u6309\u6807\u51c6&#xff0c;TCP \u53d1\u51fa\u7684 IP \u5305\u9ed8\u8ba4\u7f6e DF \u4f4d&#xff08;\u4e0d\u5141\u8bb8\u5206\u7247&#xff09;\u3002\u4e2d\u95f4\u90a3\u4e00\u8df3\u53d1\u73b0\u5305\u592a\u5927\u53c8\u4e0d\u80fd\u5206\u7247&#xff0c;\u5e94\u5f53\u56de\u4e00\u4e2a ICMP\u00a0Fragmentation Needed&#xff08;IPv6 \u662f\u00a0Packet Too Big&#xff09;&#xff0c;\u91cc\u9762\u5e26\u7740\u5b83\u7684 MTU\u3002\u53d1\u9001\u65b9\u6536\u5230\u540e\u66f4\u65b0\u8fd9\u6761\u8def\u5f84\u7684 PMTU \u4f30\u8ba1&#xff0c;\u628a\u5305\u5207\u5c0f\u91cd\u53d1\u3002\u8fd9\u5957\u673a\u5236\u53eb PMTUD&#xff0c;\u5b83\u5de5\u4f5c\u65f6\u5f88\u4f18\u96c5\u3002<\/p>\n<p>\u5b83\u4e0d\u5de5\u4f5c\u7684\u65f6\u5019&#xff0c;\u5c31\u662f\u4e0a\u9762\u90a3\u4e2a\u6545\u969c\u3002\u6574\u6761\u94fe\u8def\u4e0a\u4efb\u4f55\u4e00\u4e2a\u9632\u706b\u5899\u3001\u4efb\u4f55\u4e00\u6761\u5b89\u5168\u7ec4\u89c4\u5219\u628a ICMP \u5168\u90e8\u4e22\u6389&#xff0c;\u90a3\u4e2a\u00a0Fragmentation Needed\u00a0\u5c31\u5230\u4e0d\u4e86\u53d1\u9001\u65b9\u3002\u53d1\u9001\u65b9\u6beb\u4e0d\u77e5\u60c5&#xff0c;\u7ee7\u7eed\u6309 1460 \u53d1&#xff0c;\u5305\u5728\u4e2d\u9014\u88ab\u9759\u9ed8\u4e22\u5f03&#xff0c;\u91cd\u4f20&#xff0c;\u518d\u4e22&#xff0c;\u76f4\u5230\u00a0tcp_retries2\u00a0\u7528\u5b8c\u3002\u5c0f\u5305\u80fd\u8fc7\u662f\u56e0\u4e3a\u5b83\u4eec\u6bd4\u8def\u5f84 MTU \u5c0f&#xff0c;\u6240\u4ee5\u6574\u6761\u94fe\u8def\u4e0a\u7684\u63a7\u5236\u6d41\u91cf\u3001\u63e1\u624b\u3001\u77ed\u547d\u4ee4\u5168\u662f\u6b63\u5e38\u7684&#xff0c;\u8fd9\u5c31\u662f\u4e3a\u4ec0\u4e48\u8fd9\u7c7b\u6545\u969c\u770b\u8d77\u6765\u50cf\u300c\u7f51\u7edc\u65f6\u597d\u65f6\u574f\u300d\u3002<\/p>\n<p>IETF \u5bf9\u8fd9\u4ef6\u4e8b\u7684\u6001\u5ea6\u5728 2020 \u5e74\u6b63\u5f0f\u8f6c\u4e86\u5411\u3002RFC 8900 \u7684\u6807\u9898\u5c31\u662f\u00a0IP Fragmentation Considered Fragile&#xff0c;\u6587\u6863\u91cc\u660e\u786e\u5199\u4e86 PMTUD \u7684\u4e24\u4e2a\u8f6f\u808b&#xff1a;ICMP PTB \u7684\u77ac\u65f6\u4e22\u5931\u4f1a\u9020\u6210\u77ac\u65f6\u9ed1\u6d1e&#xff0c;\u6301\u7eed\u4e22\u5931\u4f1a\u9020\u6210\u6301\u7eed\u9ed1\u6d1e&#xff1b;\u800c\u4e14 ICMP \u6613\u4e8e\u4f2a\u9020\u3001\u63a5\u6536\u65b9\u65e0\u6cd5\u8ba4\u8bc1&#xff0c;\u653b\u51fb\u8005\u53ef\u4ee5\u628a PMTU \u4f30\u8ba1\u538b\u5230\u6781\u4f4e\u3002\u5b83\u7ed9\u4e0a\u5c42\u534f\u8bae\u7684\u5efa\u8bae\u662f\u8d70 PLPMTUD\u2014\u2014\u7531\u5206\u7ec4\u5316\u5c42\u81ea\u5df1\u53d1\u4e0d\u540c\u5927\u5c0f\u7684\u63a2\u6d4b\u5305\u5e76\u7b49\u786e\u8ba4&#xff0c;\u5b8c\u5168\u4e0d\u4f9d\u8d56\u7f51\u7edc\u4f20\u56de ICMP\u3002<\/p>\n<p>Linux \u7684\u5b9e\u73b0\u5c31\u662f\u00a0tcp_mtu_probing&#xff0c;\u6587\u6863\u5199\u5f97\u5f88\u76f4\u63a5&#xff1a;<\/p>\n<p>Controls TCP Packetization-Layer Path MTU Discovery. Takes three values: 0 &#8211; Disabled; 1 &#8211; Disabled by default, enabled when an ICMP black hole detected; 2 &#8211; Always enabled, use initial MSS of tcp_base_mss.<\/p>\n<p>\u503c 1 \u662f\u300c\u5e73\u65f6\u4e0d\u5f00&#xff0c;\u68c0\u6d4b\u5230 ICMP \u9ed1\u6d1e\u5c31\u5f00\u300d&#xff0c;\u8fd9\u662f\u7edd\u5927\u591a\u6570\u53d1\u884c\u7248\u8be5\u8bbe\u7684\u503c&#xff0c;\u800c\u4e0d\u5c11\u53d1\u884c\u7248\u7684\u9ed8\u8ba4\u4ecd\u662f 0\u3002\u5f00\u542f\u540e\u5185\u6838\u4f1a\u4ece\u00a0tcp_base_mss\u00a0\u8d77\u6b65\u4e8c\u5206\u63a2\u6d4b&#xff0c;\u4ee3\u4ef7\u662f\u63a2\u6d4b\u671f\u95f4\u7684\u51e0\u4e2a RTT \u548c\u51e0\u6b21\u91cd\u4f20\u3002\u6211\u5728\u8de8\u4e91\u4e13\u7ebf\u7684\u573a\u666f\u4e0b\u628a\u5b83\u8bbe\u6210 1&#xff0c;\u5c31\u662f\u4e3a\u4e86\u8ba9\u90a3\u7c7b\u5076\u53d1\u7684\u5927\u5305\u5361\u6b7b\u80fd\u81ea\u6108&#xff0c;\u800c\u4e0d\u662f\u7b49\u4eba\u53bb\u6293\u5305\u3002<\/p>\n<p>\u53e6\u4e00\u6761\u8def\u662f\u5728\u7f51\u5173\u4e0a\u505a MSS clamping&#xff0c;\u63e1\u624b\u5305\u4e00\u8fc7\u5c31\u628a\u5ba3\u544a\u7684 MSS \u6539\u5c0f&#xff1a;<\/p>\n<p>text<\/p>\n<p># \u628a SYN \u91cc\u5ba3\u544a\u7684 MSS \u94b3\u5230\u51fa\u63a5\u53e3 PMTU<br \/>\niptables -t mangle -A FORWARD \\\\<br \/>\n  -p tcp &#8211;tcp-flags SYN,RST SYN \\\\<br \/>\n  -j TCPMSS &#8211;clamp-mss-to-pmtu<\/p>\n<p>\u8fd9\u6761\u89c4\u5219\u6539\u7684\u662f\u63e1\u624b\u65f6\u90a3\u53e5\u8bdd\u672c\u8eab&#xff0c;\u8ba9\u4e24\u7aef\u4ece\u4e00\u5f00\u59cb\u5c31\u628a MSS \u8bb0\u5c0f\u3002\u5b83\u7ed5\u5f00\u4e86\u5bf9 ICMP \u7684\u4f9d\u8d56&#xff0c;\u4ee3\u4ef7\u662f\u6240\u6709\u7ecf\u8fc7\u8fd9\u4e2a\u7f51\u5173\u7684\u8fde\u63a5\u90fd\u8981\u4e3a\u6700\u5c0f\u7684\u90a3\u4e00\u8df3\u4e70\u5355&#xff0c;\u5373\u4fbf\u5b83\u4eec\u5b9e\u9645\u8d70\u7684\u8def\u5f84\u66f4\u5bbd\u3002VPN \u7f51\u5173\u548c\u5bb9\u5668 CNI \u91cc\u8fd9\u6761\u89c4\u5219\u51e0\u4e4e\u662f\u6807\u914d\u3002<\/p>\n<p>\u5e95\u90e8\u8fd8\u6709\u4e00\u4e2a\u5b89\u5168\u76f8\u5173\u7684\u4e0b\u754c\u503c\u5f97\u77e5\u9053\u3002TCP_MIN_MSS\u00a0\u662f 88&#xff0c;\u800c sysctl \u91cc\u53e6\u6709\u4e00\u4e2a&#xff1a;<\/p>\n<p>tcp_min_snd_mss \u2014 If this ADVMSS option is smaller than tcp_min_snd_mss, it is silently capped to tcp_min_snd_mss. Default : 48 (at least 8 bytes of payload per segment)<\/p>\n<p>\u8fd9\u4e2a\u53c2\u6570\u662f 2019 \u5e74\u90a3\u6279 SACK \u76f8\u5173\u6f0f\u6d1e\u7684\u4ea7\u7269&#xff1a;\u6076\u610f\u5bf9\u7aef\u5ba3\u544a\u4e00\u4e2a\u6781\u5c0f\u7684 MSS&#xff0c;\u80fd\u8ba9\u5185\u6838\u4e3a\u6bcf\u4e2a\u5b57\u8282\u7ef4\u62a4\u4e00\u4e2a\u6bb5&#xff0c;\u91cd\u4f20\u961f\u5217\u88ab\u6491\u7206\u3002\u9ed8\u8ba4 48 \u4fdd\u8bc1\u6bcf\u6bb5\u81f3\u5c11\u6709 8 \u5b57\u8282\u8f7d\u8377\u3002\u5b83\u662f\u4e00\u6761\u300c\u534f\u5546\u6765\u7684\u503c\u4e5f\u5f97\u6821\u9a8c\u300d\u7684\u6559\u8bad&#xff0c;\u8ddf\u6240\u6709\u4fe1\u4efb\u5916\u90e8\u8f93\u5165\u7684\u63a5\u53e3\u4e00\u4e2a\u9053\u7406\u3002<\/p>\n<p>UDP \u4fa7\u7684\u5904\u5883\u66f4\u7cdf&#xff1a;\u5b83\u6ca1\u6709 MSS \u534f\u5546&#xff0c;\u4e5f\u6ca1\u6709\u8fde\u63a5\u72b6\u6001\u53bb\u627f\u8f7d PMTU \u4f30\u8ba1\u3002\u6240\u4ee5\u57fa\u4e8e UDP \u7684\u534f\u8bae\u8981\u4e48\u81ea\u5df1\u9650\u6b7b\u5305\u957f&#xff08;DNS \u4f20\u7edf\u4e0a\u662f 512 \u5b57\u8282&#xff0c;EDNS0 \u624d\u653e\u5bbd&#xff09;&#xff0c;\u8981\u4e48\u81ea\u5df1\u505a PLPMTUD\u2014\u2014QUIC \u5c31\u662f\u540e\u8005&#xff0c;\u5b83\u628a\u63a2\u6d4b\u5199\u8fdb\u4e86\u534f\u8bae\u672c\u8eab\u3002<\/p>\n<h3>\u4e00\u4e2a\u5305\u4ece\u7f51\u7ebf\u8d70\u5230\u4f60\u7684\u8fdb\u7a0b&#xff0c;\u4e2d\u95f4\u6362\u4e86\u56db\u6b21\u624b<\/h3>\n<p>\u524d\u9762\u51e0\u8282\u8bb2\u7684\u90fd\u662f\u72b6\u6001&#xff0c;\u8fd9\u4e00\u8282\u8bb2\u72b6\u6001\u7684\u7269\u7406\u8f7d\u4f53\u3002\u628a\u5b83\u653e\u5728\u8fd9\u91cc\u7684\u7406\u7531\u662f&#xff1a;\u7b2c\u4e09\u8282\u8bf4 epoll \u7684\u5c31\u7eea\u961f\u5217\u7531\u00a0ep_poll_callback()\u00a0\u586b\u5145&#xff0c;\u800c\u90a3\u4e2a\u56de\u8c03\u7684\u8d77\u70b9&#xff0c;\u5728\u7f51\u5361\u7684 DMA \u5f15\u64ce\u4e0a\u3002<\/p>\n<p>\u63a5\u6536\u65b9\u5411\u7684\u5b8c\u6574\u94fe\u8def\u662f\u8fd9\u6837\u7684&#xff1a;<\/p>\n<p>text<\/p>\n<p> \u7f51\u7ebf<br \/>\n  \u2502 DMA \u5199\u5165<br \/>\n  \u25bc<br \/>\n RX ring \u2500\u2500 \u786c\u4e2d\u65ad \u2500\u2500\u25ba napi_schedule()<br \/>\n                          \u2502 \u5173\u6389\u8be5\u961f\u5217\u7684\u4e2d\u65ad<br \/>\n                          \u25bc<br \/>\n                   NET_RX_SOFTIRQ<br \/>\n                          \u2502<br \/>\n                   net_rx_action()<br \/>\n                          \u2502 \u9884\u7b97 300 \u5305 \/ 2000us<br \/>\n                          \u25bc<br \/>\n                   \u9a71\u52a8 poll()  \u6bcf\u5b9e\u4f8b 64 \u5305<br \/>\n                          \u2502<br \/>\n                   napi_gro_receive()  \u5408\u5e76\u8fde\u7eed\u6bb5<br \/>\n                          \u2502<br \/>\n                   netif_receive_skb() \u2192 ip_rcv()<br \/>\n                          \u2502<br \/>\n                   tcp_v4_rcv()<br \/>\n                          \u2502<br \/>\n                   sk_receive_queue  \u6216  backlog<br \/>\n                          \u2502<br \/>\n                   sk_data_ready() \u2192 ep_poll_callback()<br \/>\n                          \u2502<br \/>\n               ep-&gt;rdllist \u2190 epoll_wait \u505c\u5728\u8fd9\u91cc<\/p>\n<p>\u51e0\u4e2a\u5173\u952e\u70b9\u503c\u5f97\u9010\u4e2a\u8bf4\u3002<\/p>\n<p>\u786c\u4e2d\u65ad\u53ea\u505a\u4e00\u4ef6\u4e8b&#xff1a;\u5173\u4e2d\u65ad&#xff0c;\u7136\u540e\u8c03\u5ea6\u8f6f\u4e2d\u65ad\u3002\u00a0\u7f51\u5361\u9a71\u52a8\u5728\u4e2d\u65ad\u5904\u7406\u51fd\u6570\u91cc\u8c03\u00a0napi_schedule()&#xff0c;\u5185\u6838\u6587\u6863\u5bf9\u914d\u5957\u52a8\u4f5c\u7684\u8981\u6c42\u5f88\u660e\u786e\u2014\u2014\u300cDrivers should call this function in their interrupt handler\u300d&#xff0c;\u5e76\u4e14\u5fc5\u987b\u300ckeep the interrupts masked after scheduling the NAPI instance\u300d\u3002\u5173\u6389\u4e2d\u65ad\u662f\u91cd\u70b9&#xff1a;\u9ad8\u901f\u7f51\u5361\u4e0a\u6bcf\u5305\u4e00\u4e2a\u4e2d\u65ad\u4f1a\u8ba9 CPU \u5168\u90e8\u65f6\u95f4\u82b1\u5728\u4e0a\u4e0b\u6587\u5207\u6362\u4e0a&#xff0c;NAPI \u7684\u6838\u5fc3\u601d\u60f3\u5c31\u662f\u300c\u7b2c\u4e00\u4e2a\u5305\u7528\u4e2d\u65ad\u901a\u77e5&#xff0c;\u5269\u4e0b\u7684\u7528\u8f6e\u8be2\u53d6\u300d\u3002<\/p>\n<p>\u8f6f\u4e2d\u65ad\u6709\u9884\u7b97&#xff0c;\u8d85\u4e86\u5c31\u8fd8\u56de\u53bb\u3002\u00a0net_rx_action()\u00a0\u4e00\u8f6e\u7684\u603b\u9884\u7b97\u662f\u00a0netdev_budget&#xff0c;\u9ed8\u8ba4 300 \u4e2a\u5305&#xff1b;\u65f6\u95f4\u4e0a\u9650\u662f\u00a0netdev_budget_usecs&#xff0c;\u9ed8\u8ba4 2000 \u5fae\u79d2\u3002\u5355\u4e2a NAPI \u5b9e\u4f8b\u4e00\u8f6e\u6700\u591a\u53d6\u00a0dev_weight\u00a0\u4e2a&#xff0c;\u9ed8\u8ba4 64\u3002\u6587\u6863\u539f\u8bdd&#xff1a;\u300cPolling will exit when either netdev_budget_usecs have elapsed during the poll cycle or the number of packets processed reaches netdev_budget.\u300d<\/p>\n<p>\u9884\u7b97\u7528\u5b8c\u800c\u961f\u5217\u91cc\u8fd8\u6709\u5305\u65f6&#xff0c;net_rx_action()\u00a0\u4f1a\u91cd\u65b0 raise \u4e00\u6b21\u00a0NET_RX_SOFTIRQ\u3002\u8f6f\u4e2d\u65ad\u5728\u540c\u4e00\u6b21\u4e2d\u65ad\u8fd4\u56de\u8def\u5f84\u4e0a\u5faa\u73af\u5904\u7406\u7684\u6b21\u6570\u4e5f\u6709\u9650&#xff0c;\u8d85\u4e86\u5c31\u628a\u5269\u4e0b\u7684\u5de5\u4f5c\u4ea4\u7ed9\u00a0ksoftirqd\u00a0\u5185\u6838\u7ebf\u7a0b\u3002top\u00a0\u91cc\u00a0si\u00a0\u9ad8\u3001ksoftirqd\/N\u00a0\u5403\u6ee1\u4e00\u4e2a\u6838&#xff0c;\u8bf4\u7684\u5c31\u662f\u8fd9\u6761\u8def\u5f84\u538b\u4e0d\u4f4f\u4e86&#xff0c;\u6392\u67e5\u65b9\u5411\u662f\u00a0\/proc\/net\/softnet_stat\u00a0\u7684\u7b2c\u4e09\u5217&#xff08;time_squeeze&#xff0c;\u9884\u7b97\u8017\u5c3d\u7684\u6b21\u6570&#xff09;&#xff0c;\u800c\u4e0d\u662f\u53bb\u770b\u5e94\u7528\u7684 CPU \u706b\u7130\u56fe\u3002<\/p>\n<p>GRO \u662f\u4e00\u6b21\u6279\u91cf\u5408\u5e76\u3002\u00a0napi_gro_receive()\u00a0\u628a\u540c\u4e00\u6761\u6d41\u7684\u591a\u4e2a\u8fde\u7eed TCP \u6bb5\u62fc\u6210\u4e00\u4e2a\u5927 skb \u518d\u5f80\u4e0a\u9001&#xff0c;\u534f\u8bae\u6808\u4e0a\u5c42\u7684\u5904\u7406\u6b21\u6570\u56e0\u6b64\u4e0b\u964d\u4e00\u4e2a\u6570\u91cf\u7ea7\u3002\u5b83\u662f\u63a5\u6536\u4fa7\u7684\u6027\u80fd\u6765\u6e90&#xff0c;\u4e5f\u662f\u6293\u5305\u65f6\u770b\u5230\u300c\u4e00\u4e2a 65535 \u5b57\u8282\u7684 TCP \u6bb5\u300d\u7684\u539f\u56e0\u2014\u2014\u7ebf\u4e0a\u5e76\u6ca1\u6709\u8fd9\u4e48\u5927\u7684\u5305&#xff0c;\u90a3\u662f GRO \u5408\u5e76\u540e\u7684\u4ea7\u7269\u3002\u60f3\u770b\u771f\u5b9e\u7ebf\u4e0a\u5f62\u6001&#xff0c;\u6293\u5305\u65f6\u5f97\u5148\u00a0ethtool -K eth0 gro off\u3002<\/p>\n<p>\u534f\u8bae\u6808\u628a skb \u6302\u8fdb\u54ea\u4e2a\u961f\u5217&#xff0c;\u53d6\u51b3\u4e8e\u6b64\u523b\u7528\u6237\u6001\u6709\u6ca1\u6709\u6301\u6709\u8fd9\u4e2a socket \u7684\u9501\u3002\u00a0tcp_v4_rcv()\u00a0\u91cc\u7684\u5206\u53c9\u662f&#xff1a;socket \u6ca1\u88ab\u7528\u6237\u9501\u4f4f&#xff0c;\u76f4\u63a5\u8d70\u00a0tcp_v4_do_rcv()\u00a0\u8fdb\u00a0sk_receive_queue&#xff1b;\u88ab\u9501\u4f4f\u4e86&#xff08;\u4f60\u7684\u7ebf\u7a0b\u6b63\u5728\u00a0read\u00a0\u6216\u00a0write\u00a0\u8fd9\u6761 socket&#xff09;&#xff0c;\u5c31\u6302\u8fdb\u00a0sk_backlog&#xff0c;\u7b49\u7528\u6237\u6001\u91ca\u653e\u9501\u65f6\u518d\u5904\u7406\u3002\u8fd9\u89e3\u91ca\u4e86\u4e00\u4e2a\u73b0\u8c61&#xff1a;\u5355\u7ebf\u7a0b\u5904\u7406\u4e00\u6761\u5927\u6d41\u91cf\u8fde\u63a5\u65f6&#xff0c;\u8f6f\u4e2d\u65ad\u7684\u5de5\u4f5c\u4f1a\u88ab\u63a8\u8fdf\u5230\u4f60\u7684\u7cfb\u7edf\u8c03\u7528\u8fd4\u56de\u90a3\u4e00\u523b&#xff0c;\u5ef6\u8fdf\u5206\u5e03\u4e0a\u4f1a\u51fa\u73b0\u6bdb\u523a\u3002<\/p>\n<p>sk_data_ready\u00a0\u624d\u662f epoll \u90a3\u6761\u94fe\u7684\u8d77\u70b9\u3002\u00a0\u6570\u636e\u8fdb\u63a5\u6536\u961f\u5217\u4e4b\u540e&#xff0c;\u5185\u6838\u8c03\u7528 socket \u7684\u00a0sk_data_ready\u00a0\u56de\u8c03&#xff0c;\u5bf9\u4e8e\u88ab epoll \u76d1\u542c\u7684 fd&#xff0c;\u8fd9\u4e2a\u56de\u8c03\u6700\u7ec8\u8d70\u5230\u7b2c\u4e09\u8282\u90a3\u6bb5\u00a0ep_poll_callback()&#xff0c;\u628a epitem \u6302\u8fdb\u00a0ep-&gt;rdllist\u3002\u7b2c\u4e09\u4efd\u526f\u672c\u7684\u66f4\u65b0&#xff0c;\u5230\u8fd9\u4e00\u6b65\u624d\u53d1\u751f\u3002\u4ece DMA \u5230 rdllist&#xff0c;\u4e2d\u95f4\u9694\u7740\u4e00\u6b21\u786c\u4e2d\u65ad\u3001\u4e00\u6b21\u8f6f\u4e2d\u65ad\u8c03\u5ea6\u3001\u4e00\u6b21\u53ef\u80fd\u7684\u9884\u7b97\u8017\u5c3d\u91cd\u6392\u2014\u2014\u6240\u4ee5 epoll \u62a5\u544a\u7684\u300c\u6709\u6570\u636e\u300d&#xff0c;\u5929\u7136\u5c31\u662f\u4e00\u4e2a\u6ede\u540e\u7684\u89c2\u6d4b\u503c\u3002\u00a0\u5b83\u6ede\u540e\u591a\u4e45&#xff0c;\u53d6\u51b3\u4e8e\u8fd9\u6761\u94fe\u8def\u4e0a\u6b64\u523b\u7684\u62e5\u585e\u7a0b\u5ea6\u3002<\/p>\n<p>\u53d1\u9001\u65b9\u5411\u5bf9\u79f0\u4f46\u66f4\u77ed&#xff1a;<\/p>\n<p>text<\/p>\n<p> send()<br \/>\n  \u2502 \u62f7\u8d1d\u8fdb sk_wmem<br \/>\n  \u25bc<br \/>\n tcp_sendmsg() \u2500\u2500 \u7ec4\u88c5 sk_buff<br \/>\n  \u2502<br \/>\n tcp_write_xmit()  \u53d7 min(cwnd, rwnd) \u4e0e Nagle \u7ea6\u675f<br \/>\n  \u2502<br \/>\n GSO \/ TSO  \u2500\u2500 \u5927\u6bb5\u7559\u5230\u7f51\u5361\u518d\u5207<br \/>\n  \u2502<br \/>\n ip_queue_xmit() \u2192 qdisc &#xff08;\u6392\u961f\u89c4\u5219&#xff09;<br \/>\n  \u2502<br \/>\n dev_hard_start_xmit() \u2192 TX ring \u2192 DMA<br \/>\n  \u2502<br \/>\n \u53d1\u9001\u5b8c\u6210\u4e2d\u65ad \u2192 \u91ca\u653e skb<\/p>\n<p>TSO \u548c GSO \u662f\u53d1\u9001\u4fa7\u7684\u5bf9\u79f0\u4f18\u5316&#xff1a;\u534f\u8bae\u6808\u628a\u4e00\u4e2a\u8fdc\u5927\u4e8e MSS \u7684\u6bb5\u4e00\u8def\u5e26\u4e0b\u53bb&#xff0c;\u5207\u5206\u4ea4\u7ed9\u7f51\u5361\u786c\u4ef6\u6216\u8005\u9a71\u52a8\u7684\u672b\u7aef\u5b8c\u6210&#xff0c;\u7701\u6389\u7684\u662f\u4e0a\u5c42\u534f\u8bae\u6808\u7684\u91cd\u590d\u6267\u884c\u3002\u5b83\u8ddf\u4e0a\u4e00\u8282\u7684 MSS \u6709\u4e00\u4e2a\u4ea4\u4e92\u70b9\u2014\u2014TSO \u5f00\u7740\u7684\u65f6\u5019&#xff0c;\u6293\u5305\u770b\u5230\u7684\u6bb5\u957f\u8ddf\u7ebf\u4e0a\u5b9e\u9645\u5f62\u6001\u540c\u6837\u5bf9\u4e0d\u4e0a\u3002<\/p>\n<p>\u4e22\u5305\u70b9\u5728\u8fd9\u6761\u94fe\u4e0a\u4e00\u5171\u6709\u56db\u5904&#xff0c;\u5404\u81ea\u6709\u72ec\u7acb\u7684\u8ba1\u6570\u5668&#xff0c;\u6392\u67e5\u65f6\u6309\u987a\u5e8f\u770b\u80fd\u7701\u5f88\u591a\u65f6\u95f4&#xff1a;<\/p>\n<table>\n<tbody>\n<tr>\n<p>\u4f4d\u7f6e<\/p>\n<p>\u6ea2\u51fa\u539f\u56e0<\/p>\n<p>\u600e\u4e48\u770b<\/p>\n<\/tr>\n<tr>\n<td>\n<p>RX ring<\/p>\n<\/td>\n<td>\n<p>\u8f6f\u4e2d\u65ad\u53d6\u5305\u8ddf\u4e0d\u4e0a<\/p>\n<\/td>\n<td>\n<p>ethtool -S\u00a0\u7684\u00a0rx_dropped<\/p>\n<\/td>\n<\/tr>\n<tr>\n<td>\n<p>backlog \/ softnet<\/p>\n<\/td>\n<td>\n<p>\u9884\u7b97\u8017\u5c3d<\/p>\n<\/td>\n<td>\n<p>\/proc\/net\/softnet_stat<\/p>\n<\/td>\n<\/tr>\n<tr>\n<td>\n<p>qdisc<\/p>\n<\/td>\n<td>\n<p>\u53d1\u9001\u6392\u961f\u89c4\u5219\u6ee1<\/p>\n<\/td>\n<td>\n<p>tc -s qdisc\u00a0\u7684 dropped<\/p>\n<\/td>\n<\/tr>\n<tr>\n<td>\n<p>socket \u7f13\u51b2\u533a<\/p>\n<\/td>\n<td>\n<p>\u5e94\u7528\u8bfb\u5199\u8ddf\u4e0d\u4e0a<\/p>\n<\/td>\n<td>\n<p>ss -tanoi\u00a0\u7684 Recv-Q \/ Send-Q<\/p>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p>\u8fd9\u56db\u4e2a\u4f4d\u7f6e\u5bf9\u5e94\u56db\u79cd\u5b8c\u5168\u4e0d\u540c\u7684\u5904\u7f6e&#xff1a;\u8c03 ring \u5927\u5c0f\u3001\u8c03\u9884\u7b97\u4e0e RPS\u3001\u6362 qdisc \u6216\u9650\u901f\u3001\u6539\u5e94\u7528\u3002\u628a\u5b83\u4eec\u6df7\u6210\u4e00\u53e5\u300c\u4e22\u5305\u300d&#xff0c;\u5c31\u53ea\u80fd\u9760\u8bd5\u3002<\/p>\n<h3>UDP \u628a\u8fd9\u4e09\u4efd\u526f\u672c\u5408\u5e76\u6210\u4e86\u4f60\u624b\u91cc\u90a3\u4e00\u4efd<\/h3>\n<p>UDP \u5e38\u88ab\u8bb2\u6210\u300cTCP \u53bb\u6389\u53ef\u9760\u6027\u300d&#xff0c;\u8fd9\u4e2a\u8bf4\u6cd5\u4f1a\u8ba9\u4eba\u6f0f\u6389\u6700\u8981\u7d27\u7684\u90a3\u4ef6\u4e8b\u3002UDP \u53bb\u6389\u7684\u662f\u72b6\u6001\u672c\u8eab\u3002\u00a0\u5185\u6838\u91cc\u6ca1\u6709\u4e00\u4e2a\u5bf9\u8c61\u4ee3\u8868\u300c\u8fd9\u6761 UDP \u8fde\u63a5\u300d&#xff0c;\u4e8e\u662f\u4e09\u4efd\u526f\u672c\u584c\u7f29\u6210\u4e00\u4efd\u2014\u2014\u53ea\u5269\u4f60\u7684\u8fdb\u7a0b\u624b\u91cc\u90a3\u4efd\u8ba4\u77e5&#xff0c;\u800c\u5b83\u6ca1\u6709\u4efb\u4f55\u4e1c\u897f\u53ef\u4ee5\u4e0e\u4e4b\u5206\u6b67\u3002<\/p>\n<p>\u7531\u6b64\u53ef\u4ee5\u4e00\u6b21\u6027\u63a8\u51fa\u4e00\u4e32\u7ed3\u8bba&#xff0c;\u6bd4\u80cc\u7279\u6027\u8868\u53ef\u9760\u5f97\u591a&#xff1a;UDP \u6ca1\u6709 CLOSE_WAIT&#xff0c;\u56e0\u4e3a\u6ca1\u6709\u300c\u5bf9\u7aef\u8bf4\u5b83\u53d1\u5b8c\u4e86\u300d\u8fd9\u6761\u4fe1\u606f\u53ef\u4f20&#xff1b;\u6ca1\u6709 TIME_WAIT&#xff0c;\u56e0\u4e3a\u6ca1\u6709\u9700\u8981\u515c\u5e95\u7684\u7ec8\u7ed3 ACK&#xff1b;\u6ca1\u6709\u534a\u5f00\u72b6\u6001&#xff0c;\u56e0\u4e3a\u4e24\u7aef\u4ece\u6765\u5c31\u6ca1\u6709\u8fc7\u5171\u540c\u72b6\u6001\u53ef\u4ee5\u5931\u6b65&#xff1b;\u6ca1\u6709\u63e1\u624b&#xff0c;\u56e0\u4e3a\u6ca1\u6709\u5e8f\u53f7\u8981\u540c\u6b65&#xff1b;\u4e5f\u6ca1\u6709 MSS \u534f\u5546&#xff0c;\u56e0\u4e3a\u534f\u5546\u7ed3\u679c\u65e0\u5904\u5b58\u653e\u3002<\/p>\n<p>\u6700\u80fd\u8bf4\u660e\u95ee\u9898\u7684\u662f\u00a0connect()\u00a0\u5728\u4e24\u79cd socket \u4e0a\u7684\u5dee\u522b\u3002\u540c\u4e00\u4e2a\u7cfb\u7edf\u8c03\u7528&#xff0c;\u505a\u7684\u4e8b\u5b8c\u5168\u4e0d\u540c&#xff1a;<\/p>\n<p>C&#043;&#043;<\/p>\n<p>\/\/ TCP&#xff1a;\u771f\u7684\u53d1\u5305&#xff0c;\u4e09\u6b21\u63e1\u624b&#xff0c;\u8fd4\u56de\u65f6\u4e24\u7aef\u5185\u6838\u5404\u6709\u4e00\u4efd\u72b6\u6001<br \/>\nint fd &#061; ::socket(AF_INET, SOCK_STREAM, 0);<br \/>\n::connect(fd, addr, len);         \/\/ \u963b\u585e\u76f4\u5230\u63e1\u624b\u5b8c\u6210\u6216\u8d85\u65f6<\/p>\n<p>\/\/ UDP&#xff1a;\u4e00\u4e2a\u5305\u90fd\u4e0d\u53d1&#xff0c;\u7eaf\u672c\u5730\u64cd\u4f5c<br \/>\nint fd &#061; ::socket(AF_INET, SOCK_DGRAM, 0);<br \/>\n::connect(fd, addr, len);         \/\/ \u7acb\u5373\u8fd4\u56de<\/p>\n<p>UDP \u4e0a\u7684\u00a0connect()\u00a0\u53ea\u505a\u4e24\u4ef6\u672c\u5730\u8bb0\u8d26&#xff1a;\u5728 socket \u4e0a\u8bb0\u4e0b\u9ed8\u8ba4\u76ee\u7684\u5730\u5740&#xff0c;\u4ee5\u540e\u53ef\u4ee5\u76f4\u63a5\u7528\u00a0send()\u00a0\u800c\u4e0d\u5fc5\u6bcf\u6b21\u5e26\u00a0sendto()\u00a0\u7684\u5730\u5740&#xff1b;\u4ee5\u53ca\u628a\u8fd9\u4e2a socket \u767b\u8bb0\u8fdb\u5185\u6838\u7684\u56db\u5143\u7ec4\u67e5\u627e\u8868\u3002<\/p>\n<p>\u7b2c\u4e8c\u4ef6\u4e8b\u6709\u4e00\u4e2a\u5f88\u5c11\u88ab\u63d0\u8d77\u7684\u540e\u679c&#xff1a;\u672a connect \u7684 UDP socket \u6536\u4e0d\u5230 ICMP \u9519\u8bef\u3002\u00a0\u4f60\u00a0sendto()\u00a0\u5230\u4e00\u4e2a\u6ca1\u4eba\u76d1\u542c\u7684\u7aef\u53e3&#xff0c;\u5bf9\u7aef\u56de\u4e86\u00a0ICMP Port Unreachable&#xff0c;\u5185\u6838\u6536\u5230\u4e4b\u540e\u8981\u628a\u5b83\u5173\u8054\u56de\u67d0\u4e2a socket \u624d\u80fd\u62a5\u7ed9\u5e94\u7528&#xff0c;\u800c\u672a connect \u7684 socket \u5728\u56db\u5143\u7ec4\u8868\u91cc\u5339\u914d\u4e0d\u4e0a&#xff0c;\u4e8e\u662f\u8fd9\u4e2a\u9519\u8bef\u88ab\u4e22\u5f03&#xff0c;\u4f60\u7684\u00a0recvfrom()\u00a0\u7ee7\u7eed\u963b\u585e\u3002connect()\u00a0\u8fc7\u7684 UDP socket \u5219\u4f1a\u5728\u4e0b\u4e00\u6b21\u7cfb\u7edf\u8c03\u7528\u4e0a\u8fd4\u56de\u00a0ECONNREFUSED\u3002\u5199 UDP \u5ba2\u6237\u7aef\u65f6\u8fd9\u662f\u4e2a\u5b9e\u6253\u5b9e\u7684\u5dee\u522b&#xff1a;\u8981\u4e0d\u8981\u62ff\u5230\u300c\u5bf9\u7aef\u6ca1\u5f00\u300d\u8fd9\u4e2a\u4fe1\u606f&#xff0c;\u53d6\u51b3\u4e8e\u4f60\u6709\u6ca1\u6709\u8c03\u90a3\u4e00\u6b21\u672c\u5730\u7684\u00a0connect()\u3002<\/p>\n<p>\u5b57\u8282\u6d41\u4e0e\u6d88\u606f\u8fb9\u754c\u7684\u5dee\u522b\u4e5f\u5f52\u5230\u540c\u4e00\u5904\u3002UDP \u4fdd\u7559\u8fb9\u754c&#xff0c;\u4e00\u6b21\u00a0sendto()\u00a0\u5bf9\u5e94\u4e00\u6b21\u00a0recvfrom()&#xff1b;TCP \u662f\u5b57\u8282\u6d41&#xff0c;\u5b83\u4ece\u6765\u6ca1\u6709\u627f\u8bfa\u8fc7\u5305\u7684\u6982\u5ff5\u3002\u6240\u8c13\u300cTCP \u7c98\u5305\u300d\u8fd9\u4e2a\u8bf4\u6cd5\u672c\u8eab\u5c31\u5047\u5b9a\u4e86 TCP \u6709\u5305\u53ef\u7c98\u2014\u2014\u5b83\u6ca1\u6709\u3002\u53d1\u9001\u4fa7\u7684 Nagle \u7b97\u6cd5\u4f1a\u5408\u5e76\u5c0f\u6bb5&#xff0c;\u63a5\u6536\u4fa7\u7684 GRO \u4f1a\u5408\u5e76\u8fde\u7eed\u6bb5&#xff0c;\u4e2d\u95f4\u4efb\u4f55\u4e00\u8df3\u90fd\u53ef\u80fd\u91cd\u65b0\u5206\u6bb5\u3002\u5728\u5b57\u8282\u6d41\u4e0a\u505a\u6d88\u606f\u5207\u5206\u662f\u5e94\u7528\u5c42\u4ece\u7b2c\u4e00\u5929\u8d77\u5c31\u8be5\u505a\u7684\u4e8b&#xff0c;\u628a\u5b83\u5f53\u6210\u4e00\u4e2a\u9700\u8981\u4fee\u7684\u73b0\u8c61&#xff0c;\u65b9\u5411\u5c31\u9519\u4e86\u3002<\/p>\n<p>QUIC \u662f\u8fd9\u4e2a\u6a21\u578b\u4e0b\u6700\u503c\u5f97\u770b\u7684\u4e00\u4e2a\u53cd\u4f8b\u3002\u5b83\u8dd1\u5728 UDP \u4e0a&#xff0c;\u5374\u628a\u4e09\u4efd\u526f\u672c\u91cd\u65b0\u9020\u4e86\u4e00\u904d&#xff0c;\u53ea\u662f\u9020\u5728\u7528\u6237\u6001&#xff1a;\u8fde\u63a5\u72b6\u6001\u3001\u5e8f\u53f7\u3001\u91cd\u4f20\u3001\u62e5\u585e\u63a7\u5236\u5168\u90e8\u642c\u8fdb\u4e86\u5e94\u7528\u8fdb\u7a0b\u3002\u8fd9\u4e48\u505a\u6362\u5230\u4e86\u4e09\u6837\u4e1c\u897f\u2014\u2014\u4e0d\u5fc5\u7b49\u5185\u6838\u5347\u7ea7\u5c31\u80fd\u6539\u62e5\u585e\u7b97\u6cd5\u3001\u6d41\u4e4b\u95f4\u7684\u4e22\u5305\u4e0d\u518d\u4e92\u76f8\u963b\u585e\u3001\u4ee5\u53ca\u6700\u91cd\u8981\u7684\u4e00\u6761&#xff0c;\u8fde\u63a5\u6807\u8bc6\u4ece\u56db\u5143\u7ec4\u6362\u6210\u4e86 connection ID&#xff0c;\u4e8e\u662f\u624b\u673a\u4ece Wi-Fi \u5207\u5230\u8702\u7a9d\u3001NAT \u91cd\u65b0\u7ed1\u5b9a\u7aef\u53e3&#xff0c;\u8fde\u63a5\u90fd\u4e0d\u65ad\u3002<\/p>\n<p>\u4f46\u534a\u5f00\u53d1\u73b0\u8fd9\u4e2a\u95ee\u9898\u5728 QUIC \u91cc\u5e76\u6ca1\u6709\u6d88\u5931&#xff0c;\u53ea\u662f\u6362\u4e86\u8d1f\u8d23\u4eba\u3002QUIC \u7aef\u70b9\u5404\u81ea\u7ef4\u62a4 idle timeout \u5e76\u5728\u63e1\u624b\u65f6\u534f\u5546&#xff0c;\u9760 PING \u5e27\u7ef4\u6301\u6d3b\u6027\u2014\u2014\u8fd9\u8ddf TCP keepalive \u662f\u540c\u4e00\u5957\u903b\u8f91&#xff0c;\u533a\u522b\u53ea\u5728\u4e8e\u8d85\u65f6\u503c\u7531\u5e94\u7528\u51b3\u5b9a&#xff0c;\u53ef\u4ee5\u662f\u4e09\u5341\u79d2\u800c\u4e0d\u662f\u4e24\u5c0f\u65f6\u3002\u72b6\u6001\u526f\u672c\u7684\u4e0d\u4e00\u81f4\u662f\u5206\u5e03\u5f0f\u7cfb\u7edf\u7684\u56fa\u6709\u5c5e\u6027&#xff0c;\u6362\u4e00\u5c42\u534f\u8bae\u53ea\u80fd\u6539\u53d8\u8c01\u6765\u53d1\u73b0\u3001\u591a\u5feb\u53d1\u73b0&#xff0c;\u6d88\u4e0d\u6389\u5b83\u3002<\/p>\n<p>\u9009 UDP \u7684\u5224\u636e\u56e0\u6b64\u4e5f\u7b80\u5355&#xff1a;\u4f60\u80fd\u5bb9\u5fcd\u4e22&#xff0c;\u6216\u8005\u4f60\u6253\u7b97\u81ea\u5df1\u5b9e\u73b0\u4e00\u5957\u6bd4\u5185\u6838\u90a3\u5957\u66f4\u8d34\u5408\u4e1a\u52a1\u7684\u91cd\u4f20\u4e0e\u62e5\u585e\u7b56\u7565\u3002\u524d\u8005\u662f\u97f3\u89c6\u9891\u548c\u76d1\u63a7\u4e0a\u62a5&#xff0c;\u540e\u8005\u662f QUIC \u548c\u5404\u79cd\u81ea\u7814\u53ef\u9760 UDP\u3002\u4ecb\u4e8e\u4e24\u8005\u4e4b\u95f4\u3001\u65e2\u4e0d\u80fd\u4e22\u53c8\u4e0d\u60f3\u81ea\u5df1\u5199\u72b6\u6001\u673a\u7684\u573a\u666f&#xff0c;\u9009 UDP \u901a\u5e38\u662f\u5728\u7ed9\u81ea\u5df1\u627e\u6d3b\u5e72\u3002<\/p>\n<h3>\u4ece\u6572\u4e0b\u56de\u8f66\u5230\u9875\u9762\u51fa\u73b0&#xff0c;\u4e00\u5171\u5efa\u7acb\u548c\u62c6\u9664\u4e86\u591a\u5c11\u4efd\u72b6\u6001<\/h3>\n<p>\u628a\u524d\u9762\u6240\u6709\u7ed3\u8bba\u5957\u5230\u4e00\u6761\u771f\u5b9e\u94fe\u8def\u4e0a&#xff0c;\u95ee\u9898\u53ef\u4ee5\u6362\u4e2a\u95ee\u6cd5&#xff1a;\u4ece\u6572\u4e0b\u56de\u8f66\u5230\u9875\u9762\u51fa\u73b0&#xff0c;\u8fd9\u4e2d\u95f4\u4e00\u5171\u6709\u591a\u5c11\u4efd\u72ec\u7acb\u8001\u5316\u7684\u72b6\u6001\u526f\u672c&#xff0c;\u5404\u81ea\u7531\u8c01\u8d1f\u8d23\u53d1\u73b0\u5b83\u8fc7\u671f\u4e86\u3002<\/p>\n<p>\u57df\u540d\u89e3\u6790\u3002\u00a0\u6d4f\u89c8\u5668\u5148\u67e5\u81ea\u5df1\u7684 DNS \u7f13\u5b58\u548c HSTS \u5217\u8868&#xff0c;\u518d\u95ee\u7cfb\u7edf\u7684 stub resolver&#xff0c;\u540e\u8005\u8bfb\u00a0\/etc\/hosts\u3001\u67e5\u672c\u673a\u7f13\u5b58&#xff0c;\u672a\u547d\u4e2d\u624d\u53d1\u51fa\u771f\u6b63\u7684\u67e5\u8be2&#xff0c;\u8d70 UDP 53\u3002\u54cd\u5e94\u8d85\u8fc7\u9650\u957f\u65f6\u670d\u52a1\u7aef\u7f6e TC \u4f4d&#xff0c;\u5ba2\u6237\u7aef\u6539\u7528 TCP \u91cd\u67e5\u4e00\u904d\u2014\u2014\u8fd9\u662f DNS \u552f\u4e00\u4f1a\u7528\u5230 TCP \u7684\u5e38\u89c4\u8def\u5f84&#xff0c;EDNS0 \u628a UDP \u4e0a\u9650\u4ece 512 \u5b57\u8282\u653e\u5bbd\u4e4b\u540e\u5df2\u7ecf\u5c11\u89c1\u5f88\u591a\u3002<\/p>\n<p>\u8fd9\u4e00\u7ad9\u7684\u72b6\u6001\u526f\u672c\u662f\u00a0TTL\u3002\u6743\u5a01\u670d\u52a1\u5668\u8bf4\u8fd9\u6761\u8bb0\u5f55\u80fd\u7f13\u5b58\u4e09\u767e\u79d2&#xff0c;\u9014\u4e2d\u6bcf\u4e00\u7ea7\u9012\u5f52\u89e3\u6790\u5668\u5404\u81ea\u8ba1\u65f6&#xff0c;\u6d4f\u89c8\u5668\u8fdb\u7a0b\u5185\u53c8\u7f13\u5b58\u4e00\u4efd\u3002\u5207\u6d41\u91cf\u65f6\u6539\u4e86\u6743\u5a01\u8bb0\u5f55&#xff0c;\u5168\u7f51\u771f\u6b63\u751f\u6548\u8981\u7b49\u6700\u957f\u7684\u90a3\u4efd\u526f\u672c\u8fc7\u671f&#xff0c;\u800c\u5b83\u5230\u5e95\u6709\u591a\u957f&#xff0c;\u53d6\u51b3\u4e8e\u94fe\u8def\u4e0a\u6709\u6ca1\u6709\u54ea\u4e00\u7ea7\u628a TTL \u6539\u5c0f\u6216\u8005\u5ffd\u7565\u4e86\u3002\u300c\u6539\u4e86 DNS \u4f46\u90e8\u5206\u7528\u6237\u8fd8\u5728\u6253\u8001 IP\u300d\u8fd9\u7c7b\u73b0\u8c61&#xff0c;\u95ee\u7684\u5c31\u662f\u8fd9\u4efd\u526f\u672c\u3002<\/p>\n<p>\u90bb\u5c45\u89e3\u6790\u3002\u00a0\u76ee\u6807 IP \u4e0d\u5728\u540c\u7f51\u6bb5\u5c31\u53d1\u7ed9\u7f51\u5173&#xff0c;\u7f51\u5173\u7684 MAC \u4ece ARP \u8868\u53d6\u3002ARP \u8868\u9879\u540c\u6837\u6709\u8001\u5316\u65f6\u95f4&#xff0c;\u540c\u6837\u662f\u4e00\u4efd\u4f1a\u8fc7\u671f\u7684\u526f\u672c&#xff0c;\u540c\u6837\u5728\u5207\u6362\u7f51\u5173\u6216\u8005\u4e3b\u5907\u6f02\u79fb\u65f6\u4f1a\u51fa\u73b0\u300c\u90e8\u5206\u673a\u5668\u8fd8\u5728\u5f80\u65e7 MAC \u53d1\u300d\u3002<\/p>\n<p>NAT \u4e0e\u9632\u706b\u5899\u7684\u4f1a\u8bdd\u8868\u3002\u00a0\u8fd9\u4efd\u526f\u672c\u6700\u5bb9\u6613\u88ab\u5fd8\u6389&#xff0c;\u56e0\u4e3a\u5b83\u5728\u4f60\u7684\u673a\u5668\u4e4b\u5916\u3002\u4e2d\u95f4\u8bbe\u5907\u4e3a\u6bcf\u6761\u8fde\u63a5\u5efa\u4e00\u4e2a\u8868\u9879&#xff0c;\u4e14\u5b83\u6709\u81ea\u5df1\u7684\u8001\u5316\u65f6\u95f4&#xff0c;\u901a\u5e38\u662f\u5206\u949f\u7ea7\u3002\u8868\u9879\u8fc7\u671f\u540e&#xff0c;\u90a3\u6761 TCP \u8fde\u63a5\u5728\u4e24\u7aef\u5185\u6838\u91cc\u90fd\u8fd8\u662f ESTABLISHED&#xff0c;\u5305\u5374\u8fc7\u4e0d\u53bb\u4e86\u2014\u2014\u8fd9\u6b63\u662f\u524d\u9762\u8bb2\u7684\u7b2c\u4e8c\u79cd\u534a\u5f00\u60c5\u5f62&#xff0c;\u53d1\u73b0\u5b83\u8981\u7b49 924.6 \u79d2\u3002\u957f\u8fde\u63a5\u670d\u52a1\u7684\u5fc3\u8df3\u5468\u671f\u5fc5\u987b\u77ed\u4e8e\u94fe\u8def\u4e0a\u6700\u77ed\u7684\u90a3\u4e2a\u8001\u5316\u65f6\u95f4&#xff0c;\u8fd9\u662f\u5fc3\u8df3\u5468\u671f\u552f\u4e00\u7684\u786c\u7ea6\u675f&#xff0c;\u800c\u591a\u6570\u4eba\u662f\u6309\u7ecf\u9a8c\u62cd\u7684\u3002<\/p>\n<p>TCP \u8fde\u63a5\u672c\u8eab\u3002\u00a0\u4e00\u4e2a RTT \u7684\u63e1\u624b&#xff0c;\u6b64\u540e\u662f\u672c\u6587\u524d\u516b\u8282\u8bb2\u7684\u5168\u90e8\u5185\u5bb9\u3002<\/p>\n<p>TLS \u4f1a\u8bdd\u3002\u00a0TLS 1.3 \u628a\u5b8c\u6574\u63e1\u624b\u538b\u5230\u4e00\u4e2a RTT&#xff0c;\u4f1a\u8bdd\u6062\u590d\u80fd\u5230 0-RTT\u3002session ticket \u662f\u53c8\u4e00\u4efd\u5e26\u6709\u6548\u671f\u7684\u526f\u672c&#xff0c;\u5b83\u5b58\u5728\u5ba2\u6237\u7aef\u624b\u91cc\u3001\u7531\u670d\u52a1\u7aef\u7684\u5bc6\u94a5\u89e3\u5bc6&#xff0c;\u670d\u52a1\u7aef\u8f6e\u6362\u5bc6\u94a5\u65f6\u6240\u6709\u5728\u9014 ticket 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