{"id":103470,"date":"2026-09-10T17:49:03","date_gmt":"2026-09-10T09:49:03","guid":{"rendered":"https:\/\/www.wsisp.com\/helps\/103470.html"},"modified":"2026-09-10T17:49:03","modified_gmt":"2026-09-10T09:49:03","slug":"%e3%80%90linux%e5%86%85%e6%a0%b8%e4%b8%89%e5%8d%81%e5%85%ab%e3%80%91%e8%bf%9b%e7%a8%8b%e7%ae%a1%e7%90%86%e6%a8%a1%e5%9d%97%ef%bc%9acfs%e8%b4%9f%e8%bd%bd%e5%9d%87%e8%a1%a1%e4%b8%89%ef%bc%9a%e7%bb%84","status":"publish","type":"post","link":"https:\/\/www.wsisp.com\/helps\/103470.html","title":{"rendered":"\u3010Linux\u5185\u6838\u4e09\u5341\u516b\u3011\u8fdb\u7a0b\u7ba1\u7406\u6a21\u5757\uff1aCFS\u8d1f\u8f7d\u5747\u8861(\u4e09)\uff1a\u7ec4\u7edf\u8ba1update_sg_lb_stats\u4e0e\u6700\u5fd9\u7ec4\u6311\u9009update_sd_pick_busiest"},"content":{"rendered":"

\u5185\u6838\u7248\u672c：linux-5.15.140 \u6d89\u53ca\u6587\u4ef6：kernel\/sched\/fair.c\u3001kernel\/sched\/sched.h<\/p>\n

\u524d\u8a00<\/h3>\n

\u7b2c 37 \u7bc7\u62c6\u5b8c\u4e86 load_balance() \u4e3b\u6d41\u7a0b：should_we_balance() \u786e\u8ba4\u672c CPU \u662f\u7ec4\u5185\u4ee3\u8868\u540e，\u7b2c\u4e00\u4ef6\u6b63\u4e8b\u5c31\u662f\u8c03\u7528 find_busiest_group() \u627e\u51fa\u8be5\u8c03\u5ea6\u57df\u91cc\u6700\u5fd9\u7684\u7ec4\u3001\u5e76\u7b97\u51fa\u8be5\u642c\u591a\u5c11\u8d1f\u8f7d\u3002\u8fd9\u4e2a\u51fd\u6570\u662f\u6574\u4e2a\u8d1f\u8f7d\u5747\u8861\u7684"\u5224\u636e\u6838\u5fc3"，\u4f46\u5b83\u7684\u5b9e\u73b0\u6a2a\u8de8\u8fd1 500 \u884c：\u5148\u662f\u7edf\u8ba1（update_sd_lb_stats \u2192 update_sg_lb_stats），\u518d\u662f\u9009\u7ec4（update_sd_pick_busiest），\u7136\u540e\u662f\u5224\u5b9a（find_busiest_group \u672c\u4f53）\u4e0e\u5b9a\u91cf（calculate_imbalance），\u6700\u540e\u624d\u662f\u9009\u961f\u5217（find_busiest_queue）\u3002<\/p>\n

\u4e00\u7bc7\u585e\u4e0d\u4e0b，\u62c6\u6210\u4e24\u7bc7\u3002\u672c\u7bc7\u5148\u62c6\u524d\u534a\u573a\u2014\u2014\u7edf\u8ba1\u4e0e\u9009\u7ec4：<\/p>\n

load_balance() kernel\/sched\/fair.c:10469
\n \u2514\u2500\u2500 find_busiest_group() kernel\/sched\/fair.c:9805
\n \u2514\u2500\u2500 update_sd_lb_stats() kernel\/sched\/fair.c:9529 \u9010\u7ec4\u904d\u5386\u3001\u6c47\u603b\u57df\u7ea7\u7edf\u8ba1
\n \u251c\u2500\u2500 update_group_capacity() kernel\/sched\/fair.c:8705 \u672c\u5730\u7ec4：\u5237\u65b0\u7ec4\u5bb9\u91cf
\n \u251c\u2500\u2500 update_sg_lb_stats() kernel\/sched\/fair.c:8902 \u5355\u7ec4\u7edf\u8ba1
\n \u2502 \u2514\u2500\u2500 group_classify() kernel\/sched\/fair.c:8873 \u7ec4\u7c7b\u578b\u5206\u7ea7
\n \u2514\u2500\u2500 update_sd_pick_busiest() kernel\/sched\/fair.c:8987 \u6311\u6700\u5fd9\u7ec4<\/p>\n

find_busiest_group() \u672c\u4f53\u4e0e calculate_imbalance()\u3001find_busiest_queue() \u7559\u7ed9\u4e0b\u7bc7\u3002\u672c\u7bc7\u6240\u6709\u7ed3\u6784\u4f53\u4e0e\u51fd\u6570\u5747\u51fa\u81ea\u4e0a\u8ff0\u6e90\u7801\u4f4d\u7f6e，\u9010\u6bb5\u8d34\u539f\u6587\u3002<\/p>\n

\u4e00\u3001\u4e24\u4efd\u7edf\u8ba1\u8d26\u672c：sg_lb_stats \u4e0e sd_lb_stats<\/h3>\n

\u8d1f\u8f7d\u5747\u8861\u7684\u5224\u5b9a\u4e0d\u76f4\u63a5\u8bfb rq，\u800c\u662f\u5148\u628a\u6563\u843d\u5728\u5404 CPU \u4e0a\u7684 PELT \u4fe1\u53f7（\u89c1\u7b2c 34 \u7bc7）\u805a\u5408\u6210\u4e24\u7ea7\u7edf\u8ba1\u8d26\u672c：<\/p>\n

\/*
\n * sg_lb_stats – stats of a sched_group required for load_balancing
\n *\/<\/span>
\nstruct<\/span> sg_lb_stats<\/span> {<\/span>
\nunsigned<\/span> long<\/span> avg_load;<\/span> \/*Avg load across the CPUs of the group *\/<\/span>
\nunsigned<\/span> long<\/span> group_load;<\/span> \/* Total load over the CPUs of the group *\/<\/span>
\nunsigned<\/span> long<\/span> group_capacity;<\/span>
\nunsigned<\/span> long<\/span> group_util;<\/span> \/* Total utilization over the CPUs of the group *\/<\/span>
\nunsigned<\/span> long<\/span> group_runnable;<\/span> \/* Total runnable time over the CPUs of the group *\/<\/span>
\nunsigned<\/span> int<\/span> sum_nr_running;<\/span> \/* Nr of tasks running in the group *\/<\/span>
\nunsigned<\/span> int<\/span> sum_h_nr_running;<\/span> \/* Nr of CFS tasks running in the group *\/<\/span>
\nunsigned<\/span> int<\/span> idle_cpus;<\/span>
\nunsigned<\/span> int<\/span> group_weight;<\/span>
\nenum<\/span> group_type<\/span> group_type;<\/span>
\nunsigned<\/span> int<\/span> group_asym_packing;<\/span> \/* Tasks should be moved to preferred CPU *\/<\/span>
\nunsigned<\/span> long<\/span> group_misfit_task_load;<\/span> \/* A CPU has a task too big for its capacity *\/<\/span>
\n#<\/span>ifdef<\/span> CONFIG_NUMA_BALANCING<\/span><\/span>
\nunsigned<\/span> int<\/span> nr_numa_running;<\/span>
\nunsigned<\/span> int<\/span> nr_preferred_running;<\/span>
\n#<\/span>endif<\/span><\/span>
\n}<\/span>;<\/span><\/p>\n

kernel\/sched\/fair.c:8535<\/p>\n

sg_lb_stats \u662f\u7ec4\u7ea7\u8d26\u672c（\u4e00\u7ec4 CPU \u7684\u5408\u8ba1）：group_load\/group_util\/group_runnable \u5206\u522b\u662f\u4e09\u8def PELT \u4fe1\u53f7（load\u3001util\u3001runnable，\u89c1\u7b2c 34 \u7bc7 sched_avg）\u5728\u5168\u7ec4 CPU \u4e0a\u7684\u6c42\u548c；sum_nr_running \u6570\u6240\u6709\u4efb\u52a1，sum_h_nr_running \u53ea\u6570 CFS \u4efb\u52a1（h_nr_running \u6cbf\u5c42\u7ea7\u4f20\u64ad，\u89c1\u7b2c 35 \u7bc7）；idle_cpus \u6570\u7a7a\u95f2 CPU；group_capacity \u4e0e group_weight \u6765\u81ea\u7b2c 36 \u7bc7\u89c1\u8fc7\u7684 sched_group_capacity\u3002\u6700\u5173\u952e\u7684\u662f group_type\u2014\u2014\u672c\u7bc7\u7b2c\u4e8c\u8282\u7684\u4e3b\u89d2\u3002<\/p>\n

\/*
\n * sd_lb_stats – Structure to store the statistics of a sched_domain
\n * during load balancing.
\n *\/<\/span>
\nstruct<\/span> sd_lb_stats<\/span> {<\/span>
\nstruct<\/span> sched_group<\/span> *<\/span>busiest;<\/span>\/* Busiest group in this sd *\/<\/span>
\nstruct<\/span> sched_group<\/span> *<\/span>local;<\/span>\/* Local group in this sd *\/<\/span>
\nunsigned<\/span> long<\/span> total_load;<\/span>\/* Total load of all groups in sd *\/<\/span>
\nunsigned<\/span> long<\/span> total_capacity;<\/span>\/* Total capacity of all groups in sd *\/<\/span>
\nunsigned<\/span> long<\/span> avg_load;<\/span>\/* Average load across all groups in sd *\/<\/span>
\nunsigned<\/span> int<\/span> prefer_sibling;<\/span> \/* tasks should go to sibling first *\/<\/span><\/p>\n

struct<\/span> sg_lb_stats<\/span> busiest_stat;<\/span>\/* Statistics of the busiest group *\/<\/span>
\nstruct<\/span> sg_lb_stats<\/span> local_stat;<\/span>\/* Statistics of the local group *\/<\/span>
\n}<\/span>;<\/span><\/p>\n

kernel\/sched\/fair.c:8558<\/p>\n

sd_lb_stats \u662f\u57df\u7ea7\u8d26\u672c：\u5728\u6240\u6709\u7ec4\u7684\u5408\u8ba1\u4e4b\u4e0a，\u91cd\u70b9\u8bb0\u4e24\u4efd\u7ec4\u7ea7\u7edf\u8ba1\u2014\u2014\u672c\u5730\u7ec4（env->dst_cpu \u6240\u5728\u7ec4）\u4e0e\u6700\u5fd9\u7ec4\u3002\u6ce8\u610f busiest_stat\/local_stat \u662f\u5185\u5d4c\u7684 sg_lb_stats \u800c\u975e\u6307\u9488，\u6240\u4ee5\u521d\u59cb\u5316\u51fd\u6570\u8981\u7279\u522b\u5c0f\u5fc3：<\/p>\n

static<\/span> inline<\/span> void<\/span> init_sd_lb_stats<\/span>(<\/span>struct<\/span> sd_lb_stats<\/span> *<\/span>sds)<\/span>
\n{<\/span>
\n\/*
\n * Skimp on the clearing to avoid duplicate work. We can avoid clearing
\n * local_stat because update_sg_lb_stats() does a full clear\/assignment.
\n * We must however set busiest_stat::group_type and
\n * busiest_stat::idle_cpus to the worst busiest group because
\n * update_sd_pick_busiest() reads these before assignment.
\n *\/<\/span>
\n*<\/span>sds =<\/span> (<\/span>struct<\/span> sd_lb_stats<\/span>)<\/span>{<\/span>
\n.<\/span>busiest =<\/span> NULL<\/span>,<\/span>
\n.<\/span>local =<\/span> NULL<\/span>,<\/span>
\n.<\/span>total_load =<\/span> 0UL<\/span>,<\/span>
\n.<\/span>total_capacity =<\/span> 0UL<\/span>,<\/span>
\n.<\/span>busiest_stat =<\/span> {<\/span>
\n.<\/span>idle_cpus =<\/span> UINT_MAX,<\/span>
\n.<\/span>group_type =<\/span> group_has_spare,<\/span>
\n}<\/span>,<\/span>
\n}<\/span>;<\/span>
\n}<\/span><\/p>\n

kernel\/sched\/fair.c:8570<\/p>\n

\u4e24\u4e2a\u521d\u503c\u503c\u5f97\u73a9\u5473：idle_cpus = UINT_MAX \u8ba9\u4efb\u4f55\u771f\u5b9e\u7684\u7a7a\u95f2\u6570\u90fd"\u66f4\u5c0f"，\u914d\u5408\u7b2c\u4e94\u8282 update_sd_pick_busiest() \u4e2d group_has_spare \u5206\u652f\u7684 sgs->idle_cpus > busiest->idle_cpus \u6bd4\u8f83\u2014\u2014\u7b2c\u4e00\u4e2a\u5019\u9009\u7ec4\u5fc5\u7136\u80dc\u51fa；group_type = group_has_spare \u662f\u6700\u4f4e\u4f18\u5148\u7ea7，\u4efb\u4f55\u5019\u9009\u7ec4\u7684\u7c7b\u578b\u90fd \u2265 \u5b83\u3002\u6ce8\u91ca\u4e5f\u8bf4\u660e\u4e86\u4e3a\u4ec0\u4e48 local_stat \u4e0d\u7528\u6e05：update_sg_lb_stats() \u5f00\u5934\u6709 memset(sgs, 0, sizeof(*sgs)) \u5168\u6e05\u3002<\/p>\n

\u4e8c\u3001\u7ec4\u7684\u516d\u7ea7\u753b\u50cf：enum group_type \u4e0e group_classify<\/h3>\n

\u7edf\u8ba1\u8d26\u672c\u91cc\u6700\u8981\u7d27\u7684\u5b57\u6bb5\u662f group_type\u3002\u5185\u6838\u7ed9\u6bcf\u4e2a\u7ec4\u6253\u516d\u7ea7\u6807\u7b7e，\u679a\u4e3e\u503c\u8d8a\u5c0f\u4f18\u5148\u7ea7\u8d8a\u4f4e，\u9009\u6700\u5fd9\u7ec4\u65f6\u76f4\u63a5\u6bd4\u5927\u5c0f\u5373\u53ef：<\/p>\n

\/*
\n * 'group_type' describes the group of CPUs at the moment of load balancing.
\n *
\n * The enum is ordered by pulling priority, with the group with lowest priority
\n * first so the group_type can simply be compared when selecting the busiest
\n * group. See update_sd_pick_busiest().
\n *\/<\/span>
\nenum<\/span> group_type<\/span> {<\/span>
\n\/* The group has spare capacity that can be used to run more tasks. *\/<\/span>
\ngroup_has_spare =<\/span> 0<\/span>,<\/span>
\n\/*
\n * The group is fully used and the tasks don't compete for more CPU
\n * cycles. Nevertheless, some tasks might wait before running.
\n *\/<\/span>
\ngroup_fully_busy,<\/span>
\n\/*
\n * SD_ASYM_CPUCAPACITY only: One task doesn't fit with CPU's capacity
\n * and must be migrated to a more powerful CPU.
\n *\/<\/span>
\ngroup_misfit_task,<\/span>
\n\/*
\n * SD_ASYM_PACKING only: One local CPU with higher capacity is available,
\n * and the task should be migrated to it instead of running on the
\n * current CPU.
\n *\/<\/span>
\ngroup_asym_packing,<\/span>
\n\/*
\n * The tasks' affinity constraints previously prevented the scheduler
\n * from balancing the load across the system.
\n *\/<\/span>
\ngroup_imbalanced,<\/span>
\n\/*
\n * The CPU is overloaded and can't provide expected CPU cycles to all
\n * tasks.
\n *\/<\/span>
\ngroup_overloaded
\n}<\/span>;<\/span><\/p>\n

kernel\/sched\/fair.c:7831<\/p>\n

\u516d\u7ea7\u4ece\u597d\u5230\u574f：group_has_spare（\u6709\u5bcc\u4f59\u7b97\u529b）\u2192 group_fully_busy（\u6ee1\u8f7d\u4f46\u591f\u7528）\u2192 group_misfit_task（\u6709\u4efb\u52a1\u585e\u4e0d\u8fdb\u5c0f\u6838，\u4ec5\u5f02\u6784\u5bb9\u91cf\u57df）\u2192 group_asym_packing（\u4efb\u52a1\u8be5\u642c\u53bb\u66f4\u4f18\u5148\u7684 CPU，\u4ec5\u975e\u5bf9\u79f0\u6253\u5305\u57df）\u2192 group_imbalanced（\u6b64\u524d\u56e0\u4eb2\u548c\u6027\u7ea6\u675f\u5747\u8861\u5931\u8d25，\u6302\u4e86"\u5931\u8861\u724c"）\u2192 group_overloaded（\u8fc7\u8f7d，\u4efb\u52a1\u62a2\u4e0d\u5230\u9884\u671f\u7b97\u529b）\u3002\u8fd9\u4e2a\u987a\u5e8f\u5c31\u662f"\u503c\u5f97\u62c9\u53d6"\u7684\u4f18\u5148\u7ea7\u3002<\/p>\n

\u6253\u6807\u7b7e\u7684\u662f group_classify()，\u5224\u5b9a\u987a\u5e8f\u5373\u4f18\u5148\u7ea7\u4ece\u9ad8\u5230\u4f4e：<\/p>\n

static<\/span> inline<\/span> enum<\/span>
\ngroup_type<\/span> group_classify<\/span>(<\/span>unsigned<\/span> int<\/span> imbalance_pct,<\/span>
\n struct<\/span> sched_group<\/span> *<\/span>group,<\/span>
\n struct<\/span> sg_lb_stats<\/span> *<\/span>sgs)<\/span>
\n{<\/span>
\nif<\/span> (<\/span>group_is_overloaded<\/span>(<\/span>imbalance_pct,<\/span> sgs)<\/span>)<\/span>
\nreturn<\/span> group_overloaded;<\/span><\/p>\n

if<\/span> (<\/span>sg_imbalanced<\/span>(<\/span>group)<\/span>)<\/span>
\nreturn<\/span> group_imbalanced;<\/span><\/p>\n

if<\/span> (<\/span>sgs-><\/span>group_asym_packing)<\/span>
\nreturn<\/span> group_asym_packing;<\/span><\/p>\n

if<\/span> (<\/span>sgs-><\/span>group_misfit_task_load)<\/span>
\nreturn<\/span> group_misfit_task;<\/span><\/p>\n

if<\/span> (<\/span>!<\/span>group_has_capacity<\/span>(<\/span>imbalance_pct,<\/span> sgs)<\/span>)<\/span>
\nreturn<\/span> group_fully_busy;<\/span><\/p>\n

return<\/span> group_has_spare;<\/span>
\n}<\/span><\/p>\n

kernel\/sched\/fair.c:8873<\/p>\n

\u5176\u4e2d\u8fc7\u8f7d\u4e0e\u6709\u4f59\u91cf\u7684\u5224\u5b9a\u662f\u955c\u50cf\u7684\u4e00\u5bf9：<\/p>\n

static<\/span> inline<\/span> int<\/span> sg_imbalanced<\/span>(<\/span>struct<\/span> sched_group<\/span> *<\/span>group)<\/span>
\n{<\/span>
\nreturn<\/span> group-><\/span>sgc-><\/span>imbalance;<\/span>
\n}<\/span><\/p>\n

kernel\/sched\/fair.c:8813<\/p>\n

\/*
\n * group_has_capacity returns true if the group has spare capacity that could
\n * be used by some tasks.
\n * We consider that a group has spare capacity if the * number of task is
\n * smaller than the number of CPUs or if the utilization is lower than the
\n * available capacity for CFS tasks.
\n * For the latter, we use a threshold to stabilize the state, to take into
\n * account the variance of the tasks' load and to return true if the available
\n * capacity in meaningful for the load balancer.
\n * As an example, an available capacity of 1% can appear but it doesn't make
\n * sense for load balancer because it's in the margin of the utilization
\n *
\n *\/<\/span>
\nstatic<\/span> inline<\/span> bool
\ngroup_has_capacity<\/span>(<\/span>unsigned<\/span> int<\/span> imbalance_pct,<\/span> struct<\/span> sg_lb_stats<\/span> *<\/span>sgs)<\/span>
\n{<\/span>
\nif<\/span> (<\/span>sgs-><\/span>sum_nr_running <<\/span> sgs-><\/span>group_weight)<\/span>
\nreturn<\/span> true;<\/span><\/p>\n

if<\/span> (<\/span>(<\/span>sgs-><\/span>group_capacity *<\/span> imbalance_pct)<\/span> <<\/span>
\n(<\/span>sgs-><\/span>group_runnable *<\/span> 100<\/span>)<\/span>)<\/span>
\nreturn<\/span> false;<\/span><\/p>\n

if<\/span> (<\/span>(<\/span>sgs-><\/span>group_capacity *<\/span> 100<\/span>)<\/span> ><\/span>
\n(<\/span>sgs-><\/span>group_util *<\/span> imbalance_pct)<\/span>)<\/span>
\nreturn<\/span> true;<\/span><\/p>\n

return<\/span> false;<\/span>
\n}<\/span><\/p>\n

\/*
\n * group_is_overloaded returns true if the group has enough tasks on the
\n * cpus but still can't provide expected CPU cycles for each of them.
\n * We consider that a group is overloaded when the sum of the utilization
\n * of the CPUs is greater than the capacity of the group or the sum of the
\n * runnable of the CPUs is greater than the capacity of the group
\n *\/<\/span>
\nstatic<\/span> inline<\/span> bool
\ngroup_is_overloaded<\/span>(<\/span>unsigned<\/span> int<\/span> imbalance_pct,<\/span> struct<\/span> sg_lb_stats<\/span> *<\/span>sgs)<\/span>
\n{<\/span>
\nif<\/span> (<\/span>sgs-><\/span>sum_nr_running <=<\/span> sgs-><\/span>group_weight)<\/span>
\nreturn<\/span> false;<\/span><\/p>\n

if<\/span> (<\/span>(<\/span>sgs-><\/span>group_capacity *<\/span> 100<\/span>)<\/span> <<\/span>
\n(<\/span>sgs-><\/span>group_util *<\/span> imbalance_pct)<\/span>)<\/span>
\nreturn<\/span> true;<\/span><\/p>\n

if<\/span> (<\/span>(<\/span>sgs-><\/span>group_capacity *<\/span> imbalance_pct)<\/span> <<\/span>
\n(<\/span>sgs-><\/span>group_runnable *<\/span> 100<\/span>)<\/span>)<\/span>
\nreturn<\/span> true;<\/span><\/p>\n

return<\/span> false;<\/span>
\n}<\/span><\/p>\n

kernel\/sched\/fair.c:8818~8870`<\/p>\n

\u4e24\u4e2a\u51fd\u6570\u90fd\u9075\u5faa\u540c\u4e00\u5957\u4e09\u5c42\u5224\u5b9a，\u53ea\u662f\u6bd4\u8f83\u65b9\u5411\u76f8\u53cd：<\/p>\n

  • \u4efb\u52a1\u6570\u7c97\u7b5b：sum_nr_running \u4e0e\u7ec4\u5185 CPU \u6570（group_weight）\u6bd4\u3002\u4efb\u52a1\u6570 \u2264 CPU \u6570 \u2192 \u4e0d\u53ef\u80fd\u8fc7\u8f7d（\u6bcf CPU \u81f3\u591a\u4e00\u4e2a\u4efb\u52a1，\u76f4\u63a5 return false）；\u4efb\u52a1\u6570 < CPU \u6570 \u2192 \u5fc5\u7136\u6709\u5bcc\u4f59\u3002\u8fd9\u4e00\u5c42\u6700\u5feb，\u653e\u6700\u524d\u3002<\/li>\n
  • util \u5224\u636e：group_util（\u5b9e\u9645\u7528\u6389\u7684\u7b97\u529b）\u4e0e group_capacity \u6bd4，\u5bb9\u5dee\u7531 imbalance_pct \u63a7\u5236（\u7b2c 36 \u7bc7 sd_init \u8bbe\u7684 117，SMT \u5c42 110）\u3002\u8fc7\u8f7d\u8981\u6c42 util \u8d85\u5bb9\u91cf 17% \u4ee5\u4e0a；\u6709\u4f59\u91cf\u53cd\u8fc7\u6765\u8981\u6c42\u5bb9\u91cf\u6bd4 util \u5927 17% \u4ee5\u4e0a\u3002<\/li>\n
  • runnable \u5224\u636e：group_runnable（\u6392\u961f\u9700\u6c42）\u4e0e\u5bb9\u91cf\u6bd4\u3002runnable \u8d85\u5bb9 17% \u4e5f\u7b97\u8fc7\u8f7d\u3002<\/li>\n

    imbalance_pct \u5236\u9020\u7684\u6ede\u56de\u533a\u5f88\u5173\u952e：util \u5728\u5bb9\u91cf\u7684 \u00b117% \u533a\u95f4\u5185\u65f6\u65e2\u4e0d\u7b97\u8fc7\u8f7d\u4e5f\u4e0d\u7b97\u6709\u4f59\u91cf\u2014\u2014group_is_overloaded \u8fd4\u56de false\u3001group_has_capacity \u4e5f\u8fd4\u56de false，\u6700\u7ec8\u843d\u8fdb group_fully_busy\u3002\u8fd9\u9632\u6b62\u4e86\u8fb9\u754c\u8d1f\u8f7d\u5728\u4e24\u4e2a\u72b6\u6001\u95f4\u6296\u52a8，\u5bfc\u81f4\u5747\u8861\u5668\u6765\u56de\u642c\u4efb\u52a1\u3002\u6ce8\u91ca\u91cc\u90a3\u53e5"an available capacity of 1% can appear but it doesn\u2019t make sense"\u8bf4\u7684\u5c31\u662f：\u5bb9\u91cf\u4f59 1% \u4e0d\u503c\u5f97\u62c9\u4efb\u52a1\u8fc7\u6765\u3002<\/p>\n

    sg_imbalanced \u8bfb\u7684\u662f group->sgc->imbalance\u2014\u2014\u7b2c 37 \u7bc7 LBF_SOME_PINNED \u5584\u540e\u65f6\u5728\u7236\u57df\u7ec4\u4e0a\u7acb\u7684"\u5931\u8861\u724c"（sgc->imbalance = 1），\u4e0b\u7bc7 find_busiest_group() \u89c1\u5230\u8fd9\u4e2a\u7c7b\u578b\u4f1a\u76f4\u63a5 force_balance \u7ed5\u8fc7\u5e38\u89c4\u68c0\u67e5\u3002<\/p>\n

    \u4e09\u3001update_sg_lb_stats：\u5355\u7ec4\u9010 CPU \u7edf\u8ba1<\/h3>\n

    static<\/span> inline<\/span> void<\/span> update_sg_lb_stats<\/span>(<\/span>struct<\/span> lb_env<\/span> *<\/span>env,<\/span>
    \n struct<\/span> sched_group<\/span> *<\/span>group,<\/span>
    \n struct<\/span> sg_lb_stats<\/span> *<\/span>sgs,<\/span>
    \n int<\/span> *<\/span>sg_status)<\/span>
    \n{<\/span>
    \nint<\/span> i,<\/span> nr_running,<\/span> local_group;<\/span><\/p>\n

    memset<\/span>(<\/span>sgs,<\/span> 0<\/span>,<\/span> sizeof<\/span>(<\/span>*<\/span>sgs)<\/span>)<\/span>;<\/span><\/p>\n

    local_group =<\/span> cpumask_test_cpu<\/span>(<\/span>env-><\/span>dst_cpu,<\/span> sched_group_span<\/span>(<\/span>group)<\/span>)<\/span>;<\/span><\/p>\n

    for_each_cpu_and<\/span>(<\/span>i,<\/span> sched_group_span<\/span>(<\/span>group)<\/span>,<\/span> env-><\/span>cpus)<\/span> {<\/span>
    \nstruct<\/span> rq<\/span> *<\/span>rq =<\/span> cpu_rq<\/span>(<\/span>i)<\/span>;<\/span><\/p>\n

    sgs-><\/span>group_load +=<\/span> cpu_load<\/span>(<\/span>rq)<\/span>;<\/span>
    \nsgs-><\/span>group_util +=<\/span> cpu_util<\/span>(<\/span>i)<\/span>;<\/span>
    \nsgs-><\/span>group_runnable +=<\/span> cpu_runnable<\/span>(<\/span>rq)<\/span>;<\/span>
    \nsgs-><\/span>sum_h_nr_running +=<\/span> rq-><\/span>cfs.<\/span>h_nr_running;<\/span><\/p>\n

    nr_running =<\/span> rq-><\/span>nr_running;<\/span>
    \nsgs-><\/span>sum_nr_running +=<\/span> nr_running;<\/span><\/p>\n

    if<\/span> (<\/span>nr_running ><\/span> 1<\/span>)<\/span>
    \n*<\/span>sg_status |=<\/span> SG_OVERLOAD;<\/span><\/p>\n

    if<\/span> (<\/span>cpu_overutilized<\/span>(<\/span>i)<\/span>)<\/span>
    \n*<\/span>sg_status |=<\/span> SG_OVERUTILIZED;<\/span><\/p>\n

    #<\/span>ifdef<\/span> CONFIG_NUMA_BALANCING<\/span><\/span>
    \nsgs-><\/span>nr_numa_running +=<\/span> rq-><\/span>nr_numa_running;<\/span>
    \nsgs-><\/span>nr_preferred_running +=<\/span> rq-><\/span>nr_preferred_running;<\/span>
    \n#<\/span>endif<\/span><\/span>
    \n\/*
    \n * No need to call idle_cpu() if nr_running is not 0
    \n *\/<\/span>
    \nif<\/span> (<\/span>!<\/span>nr_running &&<\/span> idle_cpu<\/span>(<\/span>i)<\/span>)<\/span> {<\/span>
    \nsgs-><\/span>idle_cpus++<\/span>;<\/span>
    \n\/* Idle cpu can't have misfit task *\/<\/span>
    \ncontinue<\/span>;<\/span>
    \n}<\/span><\/p>\n

    if<\/span> (<\/span>local_group)<\/span>
    \ncontinue<\/span>;<\/span><\/p>\n

    \/* Check for a misfit task on the cpu *\/<\/span>
    \nif<\/span> (<\/span>env-><\/span>sd-><\/span>flags &<\/span> SD_ASYM_CPUCAPACITY &&<\/span>
    \n sgs-><\/span>group_misfit_task_load <<\/span> rq-><\/span>misfit_task_load)<\/span> {<\/span>
    \nsgs-><\/span>group_misfit_task_load =<\/span> rq-><\/span>misfit_task_load;<\/span>
    \n*<\/span>sg_status |=<\/span> SG_OVERLOAD;<\/span>
    \n}<\/span>
    \n}<\/span><\/p>\n

    \/* Check if dst CPU is idle and preferred to this group *\/<\/span>
    \nif<\/span> (<\/span>env-><\/span>sd-><\/span>flags &<\/span> SD_ASYM_PACKING &&<\/span>
    \n env-><\/span>idle !=<\/span> CPU_NOT_IDLE &&<\/span>
    \n sgs-><\/span>sum_h_nr_running &&<\/span>
    \n sched_asym_prefer<\/span>(<\/span>env-><\/span>dst_cpu,<\/span> group-><\/span>asym_prefer_cpu)<\/span>)<\/span> {<\/span>
    \nsgs-><\/span>group_asym_packing =<\/span> 1<\/span>;<\/span>
    \n}<\/span><\/p>\n

    sgs-><\/span>group_capacity =<\/span> group-><\/span>sgc-><\/span>capacity;<\/span><\/p>\n

    sgs-><\/span>group_weight =<\/span> group-><\/span>group_weight;<\/span><\/p>\n

    sgs-><\/span>group_type =<\/span> group_classify<\/span>(<\/span>env-><\/span>sd-><\/span>imbalance_pct,<\/span> group,<\/span> sgs)<\/span>;<\/span><\/p>\n

    \/* Computing avg_load makes sense only when group is overloaded *\/<\/span>
    \nif<\/span> (<\/span>sgs-><\/span>group_type ==<\/span> group_overloaded)<\/span>
    \nsgs-><\/span>avg_load =<\/span> (<\/span>sgs-><\/span>group_load *<\/span> SCHED_CAPACITY_SCALE)<\/span> \/<\/span>
    \nsgs-><\/span>group_capacity;<\/span>
    \n}<\/span><\/p>\n

    kernel\/sched\/fair.c:8902<\/p>\n

    \u9010\u6bb5\u62c6：<\/p>\n

    1. \u904d\u5386\u8303\u56f4：for_each_cpu_and(i, sched_group_span(group), env->cpus) \u53d6\u7ec4 span \u4e0e\u5747\u8861\u5019\u9009 CPU \u96c6\u5408\u7684\u4ea4\u96c6\u2014\u2014env->cpus \u5728\u7b2c 37 \u7bc7\u91cc\u5df2\u88ab LBF_ALL_PINNED \u5584\u540e\u9010\u8f6e\u5254\u9664\u642c\u4e0d\u52a8\u7684 CPU\u3002<\/p>\n

    2. \u4e09\u8def\u4fe1\u53f7\u7d2f\u52a0：cpu_load()\u3001cpu_runnable() \u76f4\u63a5\u8bfb cfs_rq \u7684 PELT \u5747\u503c：<\/p>\n

    static<\/span> unsigned<\/span> long<\/span> cpu_load<\/span>(<\/span>struct<\/span> rq<\/span> *<\/span>rq)<\/span>
    \n{<\/span>
    \nreturn<\/span> cfs_rq_load_avg<\/span>(<\/span>&<\/span>rq-><\/span>cfs)<\/span>;<\/span>
    \n}<\/span><\/p>\n

    kernel\/sched\/fair.c:5989<\/p>\n

    static<\/span> unsigned<\/span> long<\/span> cpu_runnable<\/span>(<\/span>struct<\/span> rq<\/span> *<\/span>rq)<\/span>
    \n{<\/span>
    \nreturn<\/span> cfs_rq_runnable_avg<\/span>(<\/span>&<\/span>rq-><\/span>cfs)<\/span>;<\/span>
    \n}<\/span><\/p>\n

    kernel\/sched\/fair.c:6025<\/p>\n

    cpu_util() \u7565\u590d\u6742（fair.c:6742），\u53d6 cfs_rq->avg.util_avg \u4e0e"\u5f53\u524d runnable \u4efb\u52a1\u7684\u4f30\u8ba1\u5229\u7528\u7387\u4e4b\u548c"\u7684\u8f83\u5927\u503c\u2014\u2014\u521a\u7761\u9192\u7684\u5927\u4efb\u52a1\u4e0d\u4f1a\u56e0\u4e3a\u8870\u51cf\u4e2d\u7684 util \u800c\u88ab\u4f4e\u4f30，\u8fd9\u662f EAS\/DVFS \u7684\u9700\u6c42，\u6b64\u5904\u4e0d\u5c55\u5f00\u3002<\/p>\n

    3. \u4e24\u4e2a\u72b6\u6001\u4f4d：sg_status \u662f\u672c\u57df\u7edf\u8ba1\u671f\u95f4\u7684\u805a\u5408\u6807\u5fd7，nr_running > 1 \u7f6e SG_OVERLOAD，\u4efb\u4e00 CPU cpu_overutilized() \u7f6e SG_OVERUTILIZED\u3002\u8fd9\u4e24\u4e2a\u5b8f\u5b9a\u4e49\u5728：<\/p>\n

    #<\/span>define<\/span> SG_OVERLOAD<\/span>0x1<\/span> <\/span>\/* More than one runnable task on a CPU. *\/<\/span><\/span>
    \n#<\/span>define<\/span> SG_OVERUTILIZED<\/span>0x2<\/span> <\/span>\/* One or more CPUs are over-utilized. *\/<\/span><\/span><\/p>\n

    kernel\/sched\/sched.h:785<\/p>\n

    \u5b83\u4eec\u4e0d\u662f\u7ec4\u7edf\u8ba1，\u800c\u662f\u56de\u5199\u7ed9 root_domain \u7684\u5168\u5c40\u6307\u793a\u5668（\u7b2c\u56db\u8282），\u4f9b\u5524\u9192\u9009\u6838\u8def\u5f84（check_preempt_wakeup \u4e4b\u540e\u7684 select_task_rq_fair）\u5feb\u901f\u5224\u65ad\u7cfb\u7edf\u662f\u5426\u8fc7\u8f7d\u3002<\/p>\n

    4. \u7a7a\u95f2\u8ba1\u6570：!nr_running && idle_cpu(i) \u624d\u8ba1\u5165 idle_cpus\u2014\u2014nr_running \u4e3a 0 \u662f\u5fc5\u8981\u6761\u4ef6，idle_cpu() \u518d\u786e\u8ba4 rq->curr \u662f idle \u4e14\u65e0\u5f85\u5904\u7406\u5524\u9192，\u907f\u514d\u628a\u521a\u8981\u8dd1\u4efb\u52a1\u7684 CPU \u8bef\u5224\u4e3a\u7a7a\u95f2\u3002\u6ce8\u91ca"Idle cpu can\u2019t have misfit task"\u987a\u5e26 continue \u6389\u4e86\u540e\u9762\u7684 misfit \u68c0\u67e5\u3002<\/p>\n

    5. misfit \u68c0\u67e5\u53ea\u5bf9\u975e\u672c\u5730\u7ec4\u505a：local_group \u65f6\u76f4\u63a5 continue\u3002misfit \u8bb0\u5f55\u5168\u7ec4\u6700\u5927\u7684 rq->misfit_task_load\u2014\u2014\u672c\u5730\u7ec4\u4e0d\u9700\u8981\u77e5\u9053\u81ea\u5df1\u7684 misfit（\u5747\u8861\u65b9\u5411\u662f\u628a\u4efb\u52a1\u4ece\u6700\u5fd9\u7ec4\u62c9\u5230\u672c\u5730）\u3002<\/p>\n

    6. asym_packing \u7279\u5224：\u76ee\u7684 CPU \u7a7a\u95f2\u4e14\u6bd4\u672c\u7ec4\u9996\u9009 CPU（group->asym_prefer_cpu，\u7b2c 36 \u7bc7\u62d3\u6251\u6784\u5efa\u65f6\u7b97\u597d）\u66f4\u53d7\u504f\u7231\u65f6，\u6807\u8bb0 group_asym_packing = 1，group_classify() \u636e\u6b64\u8fd4\u56de group_asym_packing \u7c7b\u578b\u3002<\/p>\n

    7. \u6536\u5c3e\u4e09\u7ea7\u8df3：\u6284\u5165\u7ec4\u5bb9\u91cf\u4e0e\u7ec4\u6743\u91cd \u2192 group_classify() \u5b9a\u578b \u2192 \u4ec5\u5f53\u8fc7\u8f7d\u65f6\u8ba1\u7b97 avg_load = group_load * 1024 \/ group_capacity\u3002\u6ce8\u91ca\u70b9\u660e：avg_load \u53ea\u5728\u8fc7\u8f7d\u6bd4\u8f83\u65f6\u6709\u610f\u4e49（\u7b2c\u4e94\u8282 group_overloaded \u5206\u652f\u62ff\u5b83 tie-break），\u975e\u8fc7\u8f7d\u7ec4\u4e0d\u7b97\u9664\u6cd5，\u7701\u4e0b\u4e00\u6b21\u5f00\u9500\u3002<\/p>\n

    \u56db\u3001update_sd_lb_stats：\u904d\u5386\u7ec4\u73af\u3001\u6c47\u603b\u57df\u8d26\u672c<\/h3>\n

    static<\/span> inline<\/span> void<\/span> update_sd_lb_stats<\/span>(<\/span>struct<\/span> lb_env<\/span> *<\/span>env,<\/span> struct<\/span> sd_lb_stats<\/span> *<\/span>sds)<\/span>
    \n{<\/span>
    \nstruct<\/span> sched_domain<\/span> *<\/span>child =<\/span> env-><\/span>sd-><\/span>child;<\/span>
    \nstruct<\/span> sched_group<\/span> *<\/span>sg =<\/span> env-><\/span>sd-><\/span>groups;<\/span>
    \nstruct<\/span> sg_lb_stats<\/span> *<\/span>local =<\/span> &<\/span>sds-><\/span>local_stat;<\/span>
    \nstruct<\/span> sg_lb_stats<\/span> tmp_sgs;<\/span>
    \nunsigned<\/span> long<\/span> sum_util =<\/span> 0<\/span>;<\/span>
    \nint<\/span> sg_status =<\/span> 0<\/span>;<\/span><\/p>\n

    do<\/span> {<\/span>
    \nstruct<\/span> sg_lb_stats<\/span> *<\/span>sgs =<\/span> &<\/span>tmp_sgs;<\/span>
    \nint<\/span> local_group;<\/span><\/p>\n

    local_group =<\/span> cpumask_test_cpu<\/span>(<\/span>env-><\/span>dst_cpu,<\/span> sched_group_span<\/span>(<\/span>sg)<\/span>)<\/span>;<\/span>
    \nif<\/span> (<\/span>local_group)<\/span> {<\/span>
    \nsds-><\/span>local =<\/span> sg;<\/span>
    \nsgs =<\/span> local;<\/span><\/p>\n

    if<\/span> (<\/span>env-><\/span>idle !=<\/span> CPU_NEWLY_IDLE ||<\/span>
    \n time_after_eq<\/span>(<\/span>jiffies,<\/span> sg-><\/span>sgc-><\/span>next_update)<\/span>)<\/span>
    \nupdate_group_capacity<\/span>(<\/span>env-><\/span>sd,<\/span> env-><\/span>dst_cpu)<\/span>;<\/span>
    \n}<\/span><\/p>\n

    update_sg_lb_stats<\/span>(<\/span>env,<\/span> sg,<\/span> sgs,<\/span> &<\/span>sg_status)<\/span>;<\/span><\/p>\n

    if<\/span> (<\/span>local_group)<\/span>
    \ngoto<\/span> next_group;<\/span><\/p>\n

    if<\/span> (<\/span>update_sd_pick_busiest<\/span>(<\/span>env,<\/span> sds,<\/span> sg,<\/span> sgs)<\/span>)<\/span> {<\/span>
    \nsds-><\/span>busiest =<\/span> sg;<\/span>
    \nsds-><\/span>busiest_stat =<\/span> *<\/span>sgs;<\/span>
    \n}<\/span><\/p>\n

    next_group:<\/span>
    \n\/* Now, start updating sd_lb_stats *\/<\/span>
    \nsds-><\/span>total_load +=<\/span> sgs-><\/span>group_load;<\/span>
    \nsds-><\/span>total_capacity +=<\/span> sgs-><\/span>group_capacity;<\/span><\/p>\n

    sum_util +=<\/span> sgs-><\/span>group_util;<\/span>
    \nsg =<\/span> sg-><\/span>next;<\/span>
    \n}<\/span> while<\/span> (<\/span>sg !=<\/span> env-><\/span>sd-><\/span>groups)<\/span>;<\/span><\/p>\n

    \/* Tag domain that child domain prefers tasks go to siblings first *\/<\/span>
    \nsds-><\/span>prefer_sibling =<\/span> child &&<\/span> child-><\/span>flags &<\/span> SD_PREFER_SIBLING;<\/span><\/p>\n

    if<\/span> (<\/span>env-><\/span>sd-><\/span>flags &<\/span> SD_NUMA)<\/span>
    \nenv-><\/span>fbq_type =<\/span> fbq_classify_group<\/span>(<\/span>&<\/span>sds-><\/span>busiest_stat)<\/span>;<\/span><\/p>\n

    if<\/span> (<\/span>!<\/span>env-><\/span>sd-><\/span>parent)<\/span> {<\/span>
    \nstruct<\/span> root_domain<\/span> *<\/span>rd =<\/span> env-><\/span>dst_rq-><\/span>rd;<\/span><\/p>\n

    \/* update overload indicator if we are at root domain *\/<\/span>
    \nWRITE_ONCE<\/span>(<\/span>rd-><\/span>overload,<\/span> sg_status &<\/span> SG_OVERLOAD)<\/span>;<\/span><\/p>\n

    \/* Update over-utilization (tipping point, U >= 0) indicator *\/<\/span>
    \nWRITE_ONCE<\/span>(<\/span>rd-><\/span>overutilized,<\/span> sg_status &<\/span> SG_OVERUTILIZED)<\/span>;<\/span>
    \ntrace_sched_overutilized_tp<\/span>(<\/span>rd,<\/span> sg_status &<\/span> SG_OVERUTILIZED)<\/span>;<\/span>
    \n}<\/span> else<\/span> if<\/span> (<\/span>sg_status &<\/span> SG_OVERUTILIZED)<\/span> {<\/span>
    \nstruct<\/span> root_domain<\/span> *<\/span>rd =<\/span> env-><\/span>dst_rq-><\/span>rd;<\/span><\/p>\n

    WRITE_ONCE<\/span>(<\/span>rd-><\/span>overutilized,<\/span> SG_OVERUTILIZED)<\/span>;<\/span>
    \ntrace_sched_overutilized_tp<\/span>(<\/span>rd,<\/span> SG_OVERUTILIZED)<\/span>;<\/span>
    \n}<\/span><\/p>\n

    update_idle_cpu_scan<\/span>(<\/span>env,<\/span> sum_util)<\/span>;<\/span>
    \n}<\/span><\/p>\n

    kernel\/sched\/fair.c:9529<\/p>\n

    1. do-while \u8d70\u7ec4\u73af：sg = sg->next \u76f4\u5230\u56de\u5230 env->sd->groups\u2014\u2014\u7b2c 36 \u7bc7\u5efa\u7684\u73af\u5f62\u94fe\u8868\u5728\u8fd9\u91cc\u6d3e\u4e0a\u7528\u573a，\u904d\u5386\u4e0d\u9700\u8981\u989d\u5916\u5bb9\u5668\u3002<\/p>\n

    2. \u672c\u5730\u7ec4\u7279\u6b8a\u5904\u7406：\u5224\u5230 env->dst_cpu \u5728\u7ec4 span \u5185，\u8bb0\u4e0b sds->local，\u4e14\u7edf\u8ba1\u76f4\u63a5\u5199\u8fdb sds->local_stat（\u4e0d\u7528 tmp \u518d\u62f7\u8d1d）\u3002\u540c\u65f6\u8d81\u673a\u5237\u65b0\u7ec4\u5bb9\u91cf：update_group_capacity()（\u7b2c 36 \u7bc7\u5df2\u62c6）\u6cbf\u5b50\u57df\u628a\u5404 CPU \u5f53\u524d\u5bb9\u91cf（\u6263\u6389 RT\/DL\/irq \u5360\u7528\u540e）\u7d2f\u8fdb sgc->capacity\u3002\u5237\u65b0\u6709\u8282\u6d41\u2014\u2014CPU_NEWLY_IDLE \u5747\u8861\u592a\u9891\u7e41，\u987b\u7b49 sgc->next_update \u5230\u70b9（\u5468\u671f\u5747\u8861\u4e0e newidle \u5747\u8861\u7684\u53d6\u820d）\u3002<\/p>\n

    3. \u975e\u672c\u5730\u7ec4\u4ea4\u7ed9 update_sd_pick_busiest() \u7ade\u9009\u6700\u5fd9\u7ec4，\u80dc\u51fa\u5219\u6574\u4f53\u62f7\u5165 sds->busiest_stat = *sgs（\u7ed3\u6784\u4f53\u8d4b\u503c，\u8fd9\u4e5f\u662f\u7b2c\u4e00\u8282\u8bf4\u5185\u5d4c\u800c\u975e\u6307\u9488\u7684\u539f\u56e0）\u3002<\/p>\n

    4. \u57df\u7ea7\u6c47\u603b：\u65e0\u8bba\u672c\u5730\u4e0e\u5426，total_load\u3001total_capacity\u3001sum_util \u4e00\u8def\u7d2f\u52a0\u2014\u2014\u4e0b\u7bc7 find_busiest_group() \u7684"\u57df\u5e73\u5747\u8d1f\u8f7d" sds->avg_load \u5c31\u4ece\u8fd9\u4e24\u4e2a total \u6765\u3002<\/p>\n

    5. prefer_sibling \u6807\u8bb0：\u5b50\u57df\u5e26 SD_PREFER_SIBLING（\u5178\u578b：MC \u5c42\u5e0c\u671b LLC \u5c3d\u91cf\u7a7a）\u65f6，\u672c\u5c42\u5747\u8861\u503e\u5411\u4e8e\u628a\u4efb\u52a1\u644a\u5230\u5144\u5f1f\u7ec4，\u4e0b\u7bc7 calculate_imbalance() \u4f1a\u7528\u5b83\u5207\u6362\u5230\u6309\u4efb\u52a1\u6570\u5bf9\u534a\u5206\u3002<\/p>\n

    6. NUMA \u573a\u666f\u7684 fbq \u5206\u7c7b：fbq_classify_group() \u6309 NUMA \u4efb\u52a1\u5360\u6bd4\u628a\u6700\u5fd9\u7ec4\u5206\u4e3a regular\/remote\/all \u4e09\u7c7b，\u5199\u8fdb env->fbq_type，\u4f9b find_busiest_queue() \u8df3\u8fc7"\u653e\u9519\u4e86\u8282\u70b9"\u7684\u961f\u5217（\u672c\u7bc7\u4e0d\u5c55\u5f00）\u3002<\/p>\n

    7. \u56de\u5199 root_domain \u6307\u793a\u5668：rd->overload（\u6709 CPU \u4e0a\u591a\u4e8e\u4e00\u4e2a runnable \u4efb\u52a1）\u53ea\u5728\u6839\u57df\u5c42（!env->sd->parent）\u5199，\u4e14\u662f\u5168\u91cf\u8d4b\u503c\u2014\u2014\u6bcf\u8f6e\u5468\u671f\u5747\u8861\u90fd\u4f1a\u91cd\u65b0\u91c7\u6837；rd->overutilized \u5219\u5728\u6839\u57df\u5168\u91cf\u5199\u3001\u5728\u975e\u6839\u5c42\u53ea\u7f6e\u4f4d\u4e0d\u6e05\u96f6（else if \u5206\u652f）\u3002overutilized \u662f EAS（\u80fd\u91cf\u611f\u77e5\u8c03\u5ea6）\u7684\u603b\u5f00\u5173\u4fe1\u53f7：\u4e00\u65e6\u4efb\u4f55\u4e00\u4e2a\u57df\u7f6e\u4f4d，\u6574\u4e2a\u7cfb\u7edf\u9000\u56de\u5e38\u89c4\u8d1f\u8f7d\u5747\u8861\u3002<\/p>\n

    8. update_idle_cpu_scan \u6536\u5c3e：\u8fd9\u4e2a\u51fd\u6570（fair.c:9452）\u7528\u4e00\u6761\u629b\u7269\u7ebf\u628a LLC \u57df\u7684 nr_idle_scan \u63d0\u793a\u5237\u65b0\u6389\u2014\u2014\u5f53 LLC \u5229\u7528\u7387\u5347\u9ad8\u65f6\u6309 y = 1024 – x\u00b2\u00b7pct\u00b2\/(10000\u00b71024) \u7f29\u51cf\u5524\u9192\u8def\u5f84 select_idle_cpu() \u7684\u626b\u63cf CPU \u6570，\u5229\u7528\u7387\u5230 85%（\u5373 imbalance_pct=117 \u7684\u5012\u6570\u9608\u503c）\u65f6\u5f52\u96f6\u505c\u6b62\u626b\u63cf\u3002\u4ec5\u5468\u671f\u5747\u8861\u65f6\u5199（newidle \u592a\u9891\u7e41，\u5199\u5171\u4eab cache line \u4ee3\u4ef7\u9ad8），\u4e14\u9700\u5f00 SIS_UTIL \u7279\u6027\u3002<\/p>\n

    \u4e94\u3001update_sd_pick_busiest：\u7ade\u9009\u6700\u5fd9\u7ec4<\/h3>\n

    static<\/span> bool update_sd_pick_busiest<\/span>(<\/span>struct<\/span> lb_env<\/span> *<\/span>env,<\/span>
    \n struct<\/span> sd_lb_stats<\/span> *<\/span>sds,<\/span>
    \n struct<\/span> sched_group<\/span> *<\/span>sg,<\/span>
    \n struct<\/span> sg_lb_stats<\/span> *<\/span>sgs)<\/span>
    \n{<\/span>
    \nstruct<\/span> sg_lb_stats<\/span> *<\/span>busiest =<\/span> &<\/span>sds-><\/span>busiest_stat;<\/span><\/p>\n

    \/* Make sure that there is at least one task to pull *\/<\/span>
    \nif<\/span> (<\/span>!<\/span>sgs-><\/span>sum_h_nr_running)<\/span>
    \nreturn<\/span> false;<\/span><\/p>\n

    \/*
    \n * Don't try to pull misfit tasks we can't help.
    \n * We can use max_capacity here as reduction in capacity on some
    \n * CPUs in the group should either be possible to resolve
    \n * internally or be covered by avg_load imbalance (eventually).
    \n *\/<\/span>
    \nif<\/span> (<\/span>sgs-><\/span>group_type ==<\/span> group_misfit_task &&<\/span>
    \n (<\/span>!<\/span>capacity_greater<\/span>(<\/span>capacity_of<\/span>(<\/span>env-><\/span>dst_cpu)<\/span>,<\/span> sg-><\/span>sgc-><\/span>max_capacity)<\/span> ||<\/span>
    \n sds-><\/span>local_stat.<\/span>group_type !=<\/span> group_has_spare)<\/span>)<\/span>
    \nreturn<\/span> false;<\/span><\/p>\n

    if<\/span> (<\/span>sgs-><\/span>group_type ><\/span> busiest-><\/span>group_type)<\/span>
    \nreturn<\/span> true;<\/span><\/p>\n

    if<\/span> (<\/span>sgs-><\/span>group_type <<\/span> busiest-><\/span>group_type)<\/span>
    \nreturn<\/span> false;<\/span><\/p>\n

    \/*
    \n * The candidate and the current busiest group are the same type of
    \n * group. Let check which one is the busiest according to the type.
    \n *\/<\/span><\/p>\n

    switch<\/span> (<\/span>sgs-><\/span>group_type)<\/span> {<\/span>
    \ncase<\/span> group_overloaded:<\/span>
    \n\/* Select the overloaded group with highest avg_load. *\/<\/span>
    \nif<\/span> (<\/span>sgs-><\/span>avg_load <=<\/span> busiest-><\/span>avg_load)<\/span>
    \nreturn<\/span> false;<\/span>
    \nbreak<\/span>;<\/span><\/p>\n

    case<\/span> group_imbalanced:<\/span>
    \n\/*
    \n * Select the 1st imbalanced group as we don't have any way to
    \n * choose one more than another.
    \n *\/<\/span>
    \nreturn<\/span> false;<\/span><\/p>\n

    case<\/span> group_asym_packing:<\/span>
    \n\/* Prefer to move from lowest priority CPU's work *\/<\/span>
    \nif<\/span> (<\/span>sched_asym_prefer<\/span>(<\/span>sg-><\/span>asym_prefer_cpu,<\/span> sds-><\/span>busiest-><\/span>asym_prefer_cpu)<\/span>)<\/span>
    \nreturn<\/span> false;<\/span>
    \nbreak<\/span>;<\/span><\/p>\n

    case<\/span> group_misfit_task:<\/span>
    \n\/*
    \n * If we have more than one misfit sg go with the biggest
    \n * misfit.
    \n *\/<\/span>
    \nif<\/span> (<\/span>sgs-><\/span>group_misfit_task_load <<\/span> busiest-><\/span>group_misfit_task_load)<\/span>
    \nreturn<\/span> false;<\/span>
    \nbreak<\/span>;<\/span><\/p>\n

    case<\/span> group_fully_busy:<\/span>
    \n\/*
    \n * Select the fully busy group with highest avg_load. In
    \n * theory, there is no need to pull task from such kind of
    \n * group because tasks have all compute capacity that they need
    \n * but we can still improve the overall throughput by reducing
    \n * contention when accessing shared HW resources.
    \n *
    \n * XXX for now avg_load is not computed and always 0 so we
    \n * select the 1st one.
    \n *\/<\/span>
    \nif<\/span> (<\/span>sgs-><\/span>avg_load <=<\/span> busiest-><\/span>avg_load)<\/span>
    \nreturn<\/span> false;<\/span>
    \nbreak<\/span>;<\/span><\/p>\n

    case<\/span> group_has_spare:<\/span>
    \n\/*
    \n * Select not overloaded group with lowest number of idle cpus
    \n * and highest number of running tasks. We could also compare
    \n * the spare capacity which is more stable but it can end up
    \n * that the group has less spare capacity but finally more idle
    \n * CPUs which means less opportunity to pull tasks.
    \n *\/<\/span>
    \nif<\/span> (<\/span>sgs-><\/span>idle_cpus ><\/span> busiest-><\/span>idle_cpus)<\/span>
    \nreturn<\/span> false;<\/span>
    \nelse<\/span> if<\/span> (<\/span>(<\/span>sgs-><\/span>idle_cpus ==<\/span> busiest-><\/span>idle_cpus)<\/span> &&<\/span>
    \n (<\/span>sgs-><\/span>sum_nr_running <=<\/span> busiest-><\/span>sum_nr_running)<\/span>)<\/span>
    \nreturn<\/span> false;<\/span><\/p>\n

    break<\/span>;<\/span>
    \n}<\/span><\/p>\n

    \/*
    \n * Candidate sg has no more than one task per CPU and has higher
    \n * per-CPU capacity. Migrating tasks to less capable CPUs may harm
    \n * throughput. Maximize throughput, power\/energy consequences are not
    \n * considered.
    \n *\/<\/span>
    \nif<\/span> (<\/span>(<\/span>env-><\/span>sd-><\/span>flags &<\/span> SD_ASYM_CPUCAPACITY)<\/span> &&<\/span>
    \n (<\/span>sgs-><\/span>group_type <=<\/span> group_fully_busy)<\/span> &&<\/span>
    \n (<\/span>capacity_greater<\/span>(<\/span>sg-><\/span>sgc-><\/span>min_capacity,<\/span> capacity_of<\/span>(<\/span>env-><\/span>dst_cpu)<\/span>)<\/span>)<\/span>)<\/span>
    \nreturn<\/span> false;<\/span><\/p>\n

    return<\/span> true;<\/span>
    \n}<\/span><\/p>\n

    kernel\/sched\/fair.c:8987<\/p>\n

    \u8fd9\u662f\u672c\u7bc7\u6700\u7cbe\u5f69\u7684\u51fd\u6570，\u7ade\u9009\u89c4\u5219\u5206\u56db\u5c42：<\/p>\n

    \u7b2c 1 \u5c42：\u4e00\u7968\u5426\u51b3\u3002sum_h_nr_running == 0（\u7ec4\u91cc\u6ca1\u6709 CFS \u4efb\u52a1）\u76f4\u63a5\u51fa\u5c40\u3002misfit \u7c7b\u578b\u4e5f\u6709\u4e00\u7968\u5426\u51b3：\u672c\u5730 CPU \u5bb9\u91cf\u4e0d\u6bd4\u8be5\u7ec4\u6700\u5927\u5bb9\u91cf\u660e\u663e\u66f4\u5927（capacity_greater \u5b8f，fair.c:122，(cap1)*1024 > (cap2)*1078，\u5373 cap1 \u987b\u8d85\u51fa\u7ea6 5% \u624d\u7b97"\u66f4\u5927"），\u6216\u672c\u5730\u7ec4\u81ea\u5df1\u90fd\u6ca1\u6709\u5bcc\u4f59\u2014\u2014\u62c9\u8fc7\u6765\u4e5f\u89e3\u51b3\u4e0d\u4e86 misfit，\u767d\u642c\u3002<\/p>\n

    \u7b2c 2 \u5c42：\u7c7b\u578b\u6bd4\u5927\u5c0f\u3002group_type \u679a\u4e3e\u503c\u5927\u7684\u76f4\u63a5\u80dc\u51fa（\u8fc7\u8f7d > \u5931\u8861\u724c > \u2026\u2026），\u8fd9\u6b63\u662f\u7b2c\u4e00\u8282\u6ce8\u91ca"ordered by pulling priority"\u7684\u7528\u610f\u2014\u2014\u9009\u6700\u5fd9\u7ec4\u9000\u5316\u6210\u4e00\u6b21\u6574\u6570\u6bd4\u8f83\u3002<\/p>\n

    \u7b2c 3 \u5c42：\u540c\u578b tie-break，\u6bcf\u79cd\u7c7b\u578b\u6709\u81ea\u5df1\u7684"\u66f4\u5fd9"\u6807\u51c6：<\/p>\n

      \n
    • group_overloaded：\u6bd4 avg_load（\u7b2c\u4e09\u8282\u91cc\u53ea\u5728\u8fc7\u8f7d\u65f6\u624d\u8ba1\u7b97\u7684\u9664\u6cd5\u7ed3\u679c）；<\/li>\n
    • group_imbalanced：\u62ff\u7b2c\u4e00\u4e2a（\u6ca1\u6709\u53ef\u6bd4\u6027）；<\/li>\n
    • group_asym_packing：\u6bd4\u8c01\u7684 asym_prefer_cpu \u4f18\u5148\u7ea7\u66f4\u4f4e（\u66f4\u4f4e\u4f18\u5148 CPU \u4e0a\u7684\u6d3b\u66f4\u8be5\u642c\u8d70）；<\/li>\n
    • group_misfit_task：\u6bd4\u6700\u5927\u7684 misfit \u8d1f\u8f7d；<\/li>\n
    • group_fully_busy：\u6ce8\u91ca\u5766\u8bda\u8bf4\u7406\u2014\u2014\u6ee1\u8f7d\u7ec4\u4efb\u52a1\u7b97\u529b\u672c\u6765\u5c31\u591f，\u7406\u8bba\u4e0a\u4e0d\u7528\u62c9，\u4f46\u62c9\u4e00\u70b9\u80fd\u51cf\u5c11\u5171\u4eab\u786c\u4ef6\u8d44\u6e90（cache）\u4e89\u7528，\u63d0\u5347\u541e\u5410；\u4e0d\u8fc7 avg_load \u6b64\u523b\u6052\u4e3a 0（\u7b2c\u4e09\u8282\u53ea\u5728 overloaded \u65f6\u7b97），\u6240\u4ee5\u5b9e\u9645\u9009\u7b2c\u4e00\u4e2a，\u6ce8\u91ca\u91cc\u7559\u7740 XXX \u6807\u8bb0；<\/li>\n
    • group_has_spare：\u6bd4 idle_cpus \u5c11\u7684（\u7a7a\u95f2 CPU \u5c11 = \u66f4"\u6ee1"），\u5e73\u624b\u518d\u6bd4 sum_nr_running \u591a\u7684\u3002\u6ce8\u91ca\u89e3\u91ca\u4e86\u4e3a\u4ec0\u4e48\u4e0d\u7528\u66f4\u7a33\u5b9a\u7684"\u5bcc\u4f59\u5bb9\u91cf"\u6bd4：\u5bb9\u91cf\u5c0f\u4f46\u7a7a\u95f2 CPU \u591a\u7684\u7ec4，\u53cd\u800c\u66f4\u4e0d\u503c\u5f97\u4ece\u5b83\u62c9\u4efb\u52a1\u2014\u2014\u5747\u8861\u7684\u672c\u8d28\u662f\u6d88\u706d\u7a7a\u95f2 CPU\u3002<\/li>\n<\/ul>\n

      \u7b2c 4 \u5c42：\u541e\u5410\u4fdd\u62a4\u3002\u5f02\u6784\u5bb9\u91cf\u57df\u4e0a，\u5019\u9009\u7ec4\u867d\u7136\u53ea\u6709"\u6bcf CPU \u81f3\u591a\u4e00\u4e2a\u4efb\u52a1"\u7684\u8f7b\u5ea6\u8d1f\u8f7d，\u4f46\u5176\u6700\u5c0f\u5bb9\u91cf CPU \u90fd\u6bd4\u672c\u5730 CPU \u5f3a 5% \u4ee5\u4e0a\u65f6，\u628a\u4efb\u52a1\u62c9\u5230\u5f31 CPU \u4e0a\u4f1a\u635f\u5bb3\u541e\u5410\u2014\u2014\u76f4\u63a5\u5426\u51b3\u3002\u6ce8\u91ca\u660e\u786e"Maximize throughput, power\/energy consequences are not considered"\u3002<\/p>\n

      \u5c0f\u7ed3<\/h3>\n
    • \u4e24\u7ea7\u8d26\u672c：sg_lb_stats（\u7ec4\u7ea7：\u4e09\u8def PELT \u4fe1\u53f7\u6c42\u548c + \u4efb\u52a1\u6570 + \u7a7a\u95f2\u6570 + \u7c7b\u578b）\u4e0e sd_lb_stats（\u57df\u7ea7：\u672c\u5730\u7ec4\u4e0e\u6700\u5fd9\u7ec4\u4e24\u4efd\u7ec4\u8d26\u672c + \u5168\u57df total\/avg），init_sd_lb_stats \u7528"\u6700\u574f\u521d\u503c"（idle_cpus=UINT_MAX\u3001group_type=group_has_spare）\u4fdd\u8bc1\u9996\u4e2a\u5019\u9009\u7ec4\u5fc5\u7136\u5f53\u9009\u3002<\/li>\n
    • \u516d\u7ea7\u7c7b\u578b\u753b\u50cf：group_type \u6309"\u503c\u5f97\u62c9\u53d6\u7684\u4f18\u5148\u7ea7"\u6392\u5e8f（has_spare \u2192 fully_busy \u2192 misfit \u2192 asym_packing \u2192 imbalanced \u2192 overloaded），group_classify \u4f9d\u5e8f\u5224\u5b9a；imbalance_pct（\u9ed8\u8ba4 117）\u5728\u8fc7\u8f7d\/\u6709\u4f59\u91cf\u4e4b\u95f4\u5236\u9020 \u00b117% \u7684\u6ede\u56de\u533a，\u843d\u5165\u5176\u4e2d\u7684\u7ec4\u662f group_fully_busy\u3002<\/li>\n
    • update_sg_lb_stats \u9010 CPU \u7d2f\u52a0\u4e09\u8def\u4fe1\u53f7\u3001\u7f6e SG_OVERLOAD\/SG_OVERUTILIZED \u72b6\u6001\u4f4d\u3001\u8bb0 misfit \u4e0e asym_packing\u3001\u6570\u7a7a\u95f2 CPU，\u6700\u540e\u5b9a\u578b group_type；avg_load \u53ea\u5728\u8fc7\u8f7d\u65f6\u624d\u505a\u9664\u6cd5\u3002<\/li>\n
    • update_sd_lb_stats \u6cbf\u7ec4\u73af do-while \u904d\u5386：\u672c\u5730\u7ec4\u987a\u8def\u8282\u6d41\u5237\u65b0 update_group_capacity，\u975e\u672c\u5730\u7ec4\u7ade\u9009\u6700\u5fd9\u7ec4，\u5168\u57df\u7d2f\u52a0 total；\u6839\u57df\u5c42\u56de\u5199 rd->overload\/rd->overutilized \u6307\u793a\u5668（overutilized \u662f EAS \u7684\u603b\u5f00\u5173）；update_idle_cpu_scan \u7528\u629b\u7269\u7ebf\u8c03\u5524\u9192\u626b\u63cf\u63d0\u793a\u3002<\/li>\n
    • update_sd_pick_busiest \u56db\u5c42\u7ade\u9009：\u65e0\u4efb\u52a1\/misfit \u65e0\u89e3\u4e00\u7968\u5426\u51b3 \u2192 \u7c7b\u578b\u6bd4\u5927\u5c0f \u2192 \u540c\u578b tie-break（\u5404\u7c7b\u578b\u5404\u6709\u4e00\u628a\u5c3a）\u2192 \u5f02\u6784\u57df\u541e\u5410\u4fdd\u62a4\u3002<\/li>\n

      \u7edf\u8ba1\u4e0e\u9009\u7ec4\u5b8c\u6210\u540e，sds \u91cc\u5df2\u7ecf\u8eba\u7740\u5b8c\u6574\u7684\u5019\u9009\u540d\u5355\u3002\u4e0b\u7bc7\u8fdb\u5165 find_busiest_group() \u672c\u4f53：\u516d\u79cd\u672c\u5730\u00d7\u6700\u5fd9\u7c7b\u578b\u7ec4\u5408\u7684\u51b3\u7b56\u77e9\u9635\u3001calculate_imbalance() \u600e\u4e48\u628a"\u8be5\u4e0d\u8be5\u642c"\u7ffb\u8bd1\u6210"\u642c\u591a\u5c11"（migrate_load\/util\/task\/misfit \u56db\u79cd\u6a21\u5f0f），\u4ee5\u53ca find_busiest_queue() \u5728\u6700\u5fd9\u7ec4\u5185\u6311\u51fa\u5177\u4f53\u6e90\u961f\u5217\u3002<\/p>\n

      \n

      \u7cfb\u5217\u56de\u94fe：load_balance \u4e3b\u6d41\u7a0b\u4e0e lb_env \u89c1[\u7b2c 37 \u7bc7]；sched_group\/sched_group_capacity \u7ed3\u6784\u4e0e\u7ec4\u73af\u94fe\u89c1[\u7b2c 36 \u7bc7]；PELT \u4e09\u8def\u4fe1\u53f7（load\/util\/runnable）\u89c1[\u7b2c 34 \u7bc7]；h_nr_running \u5c42\u7ea7\u4f20\u64ad\u4e0e removed \u673a\u5236\u89c1[\u7b2c 35 \u7bc7]；sched_asym_prefer \u4e0e asym_prefer_cpu \u89c1[\u7b2c 36 \u7bc7]\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"

      \u5185\u6838\u7248\u672c：linux-5.15.140 \u6d89\u53ca\u6587\u4ef6：kernel\/sched\/fair.c\u3001kernel\/sched\/sched.h \u524d\u8a00
      \n\u7b2c 37 \u7bc7\u62c6\u5b8c\u4e86 load_balance() \u4e3b\u6d41\u7a0b：should_we_balance() \u786e\u8ba4\u672c CPU \u662f\u7ec4\u5185\u4ee3\u8868\u540e，\u7b2c\u4e00\u4ef6\u6b63\u4e8b\u5c31\u662f\u8c03\u7528 find_busiest_group() \u627e\u51fa\u8be5\u8c03\u5ea6\u57df\u91cc\u6700\u5fd9\u7684\u7ec4\u3001\u5e76\u7b97\u51fa\u8be5\u642c\u591a\u5c11\u8d1f\u8f7d\u3002\u8fd9\u4e2a\u51fd\u6570\u662f\u6574\u4e2a\u8d1f\u8f7d\u5747\u8861\u7684\\”\u5224\u636e\u6838\u5fc3\\”&#xff0c<\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[58,427,258],"topic":[],"class_list":["post-103470","post","type-post","status-publish","format-standard","hentry","category-server","tag-linux","tag-427","tag-258"],"yoast_head":"\n\u3010Linux\u5185\u6838\u4e09\u5341\u516b\u3011\u8fdb\u7a0b\u7ba1\u7406\u6a21\u5757\uff1aCFS\u8d1f\u8f7d\u5747\u8861(\u4e09)\uff1a\u7ec4\u7edf\u8ba1update_sg_lb_stats\u4e0e\u6700\u5fd9\u7ec4\u6311\u9009update_sd_pick_busiest - 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