Quoting Tvrtko Ursulin (2018-02-21 09:11:15)
>
> On 20/02/2018 21:40, Chris Wilson wrote:
> > Rather than iteratively disable and then immediately reenable a CPU,
> > turn off each in turn, forcing the PMU events onto the next CPU without
> > allowing them to retreat back to CPU0 after the first. If this fails,
>
> Hm, interesting and I think it possibly makes sense to test both
> migration patterns.
Yup.
> > @@ -988,35 +999,43 @@ static void cpu_hotplug(int gem_fd)
> > */
> > igt_fork(child, 1) {
> > int cpu = 0;
> > + int cpufd;
> > + int err;
> >
> > close(link[0]);
> >
> > + /* Offline each cpu in turn */
> > for (;;) {
> > - char name[128];
> > - int cpufd;
> > -
> > - igt_assert_lt(snprintf(name, sizeof(name),
> > - "/sys/devices/system/cpu/cpu%d/online",
> > - cpu), sizeof(name));
> > - cpufd = open(name, O_WRONLY);
> > - if (cpufd == -1) {
> > - igt_assert(cpu > 0);
> > - /*
> > - * Signal parent that we cycled through all
> > - * CPUs and we are done.
> > - */
> > - igt_assert_eq(write(link[1], "*", 1), 1);
> > + cpufd = open_cpu_online(cpu);
> > + igt_assert(cpufd != -1);
> > +
> > + err = write(cpufd, "0", 2);
> > + close(cpufd);
> > + if (err < 0)
> > break;
>
> Keep off-lining until no more CPUs to offline? I had to try it! :) Ok,
> last one will fail to offline. But I think it needs a comment.
I thought that was a fun trick to try and offline the last cpu :)
> > - }
> >
> > - /* Offline followed by online a CPU. */
> > - igt_assert_eq(write(cpufd, "0", 2), 2);
> > usleep(1e6);
> > - igt_assert_eq(write(cpufd, "1", 2), 2);
> > + cpu++;
> > + }
> >
> > + /* Then bring them back online */
> > + while (cpu--) {
> > + cpufd = open_cpu_online(cpu);
> > + err = write(cpufd, "1", 2);
> > close(cpufd);
>
> Need to online in the same order or the PMU will stay on some higher CPU
> making the subsequent tests fail. Or I need to improve the helpers to
> hunt for the correct CPU, as perf tool does.
Ah. I was expecting everytime we onlined a new cpu, the notifier would
move the pmu. Why do the subsequent tests fail? In my naivety I expected
one CPU is as good as any other for pmu. Do we need to put a trivial
test inside the online/offline loops?
-Chris
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