linux – 编写系统调用来计算进程的上下文切换

wait3 syscall或getrusage syscall已报告struct rusage字段中的上下文切换计数：

struct rusage {
 ...
    long   ru_nvcsw;         /* voluntary context switches */
    long   ru_nivcsw;        /* involuntary context switches */
};

您可以通过运行来尝试：

$/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.

通过在内核源代码中搜索“struct rusage”,您可以在kernel / sys.c中找到更新rusage结构的this accumulate_thread_rusage.它从struct task_struct * t读取;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;

然后你应该在kernel文件夹中搜索nvcsw和nivcsw来查找内核如何更新它们.

asmlinkage void __sched schedule(void)：

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 */

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

PS：来自perreal的链接很棒：http://oreilly.com/catalog/linuxkernel/chapter/ch10.html(搜索context_swtch)