解决方法
如果您的系统调用只应报告统计信息,则可以使用内核中已有的上下文切换计数代码.
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)