On 06/19, Oleg Nesterov wrote:
>
> On 06/19, Peter Zijlstra wrote:
> >
> > I'm probably missing something obviuos, but what are we trying to do?
>
> Say, "perf record -e sched:sched_switch -p1".
>
> Every task except /sbin/init will do perf_trace_sched_switch() and
> perf_trace_buf_prepare() + perf_trace_buf_submit for no reason(),
> it doesn't have a counter.
I did some testing under kvm, not sure these numbers actually mean
something, but still.
So, the test-case:
int pipe1[2], pipe2[2];
void *tfunc(void *arg)
{
for (;;) {
char c;
assert(read(pipe1[0], &c, 1) == 1);
assert(write(pipe2[1], &c, 1) == 1);
}
}
int main(void)
{
pthread_t thr;
int nr;
assert(pipe(pipe1) == 0);
assert(pipe(pipe2) == 0);
assert(pthread_create(&thr, NULL, tfunc, NULL) == 0);
for (nr = 0; nr < 1000 * 1000; ++nr) {
char c;
assert(write(pipe1[1], &c, 1) == 1);
assert(read(pipe2[0], &c, 1) == 1);
}
return 0;
}
Idle machine, "/usr/bin/time -f "%e %S %U" taskset 1 ./pf" 3 times:
20.73 20.05 0.66
20.68 20.04 0.63
20.68 20.02 0.65
Now with "perf record -e sched:sched_switch -p1" running,
before 3/3:
21.59 20.77 0.80
21.40 20.70 0.68
21.50 20.72 0.78
after 3/3:
21.00 20.23 0.76
20.89 20.19 0.69
20.94 20.26 0.66
Oleg.
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