如果您的系統調用只應報告統計信息,則可以使用內核中已有的上下文切換計數代碼.

struct rusage {

...

long ru_nvcsw; /* voluntary context switches */

long ru_nivcsw; /* involuntary context switches */

};

您可以通過運行來嘗試：

$/usr/bin/time -v /bin/ls -R

....

Voluntary context switches: 1669

Involuntary context switches: 207

其中“/ bin / ls -R”是任何程序.

通過在內核源代碼中搜索“struct rusage”,您可以在kernel / sys.c中找到更新rusage結構的this accumulate_thread_rusage.它從struct task_struct * t讀取;字段t-> nvcsw;和t-> nivcsw;：

1477 static void accumulate_thread_rusage(struct task_struct *t,struct rusage *r)

1478 {

1479 r->ru_nvcsw += t->nvcsw; // <<=== here

1480 r->ru_nivcsw += t->nivcsw;

1481 r->ru_minflt += t->min_flt;

1482 r->ru_majflt += t->maj_flt;

然后你應該在kernel文件夾中搜索nvcsw和nivcsw來查找內核如何更新它們.

4124 if (likely(prev != next)) { // <= if we are switching between different tasks

4125 sched_info_switch(prev,next);

4126 perf_event_task_sched_out(prev,next);

4127

4128 rq->nr_switches++;

4129 rq->curr = next;

4130 ++*switch_count; // <= increment nvcsw or nivcsw via pointer

4131

4132 context_switch(rq,prev,next); /* unlocks the rq */

指針switch_count是同一文件的line 4091或line 4111.