Hi Chris,
On Fri, 2020-05-08 at 18:54 +0100, Chris Wilson wrote:
> Quoting Janusz Krzysztofik (2020-05-08 14:56:31)
> > static double nop_on_ring(int fd, uint32_t handle,
> > const struct intel_execution_engine2 *e, int timeout,
> > - unsigned long *out)
> > + unsigned long *count)
> > {
> > struct drm_i915_gem_execbuffer2 execbuf;
> > struct drm_i915_gem_exec_object2 obj;
> > struct timespec start, now;
> > - unsigned long count;
> > + unsigned long total;
> > +
> > + igt_assert(*count);
> >
> > memset(&obj, 0, sizeof(obj));
> > obj.handle = handle;
> > @@ -93,18 +95,18 @@ static double nop_on_ring(int fd, uint32_t handle,
> > }
> > intel_detect_and_clear_missed_interrupts(fd);
> >
> > - count = 0;
> > + total = 0;
> > clock_gettime(CLOCK_MONOTONIC, &start);
> > do {
> > - for (int loop = 0; loop < 1024; loop++)
> > + for (int loop = 0; loop < *count; loop++)
>
> This unnerves me. I expect to get this wrong when writing new callers.
>
> There's no great reason to even have 1024 here, we can survive with
> doing clock_gettime() every iteration, and just accept it as part of the
> systematic cost.
Thanks for fixing this and merging the change.
Following our discussion on IRC which I probably didn't understand
precisely enough but maybe have a better understanding now after having
it reread, how about still addressing the "headless" requirement for
better precision with the following hunk?
@@ -373,10 +372,12 @@ stable_nop_on_ring(int fd, uint32_t handle,
while (reps--) {
unsigned long count;
double time;
time = nop_on_ring(fd, handle, e, timeout, &count);
+ igt_skip_on_f(count < 1000 * timeout,
+ "submicrosecond precision of time measurement\n");
igt_stats_push_float(&s, time / count);
}
n = igt_stats_get_median(&s);
igt_stats_fini(&s);
Thanks,
Janusz
> >
> > - count += 1024;
> > + total += *count;
> > clock_gettime(CLOCK_MONOTONIC, &now);
> > } while (elapsed(&start, &now) < timeout);
> > igt_assert_eq(intel_detect_and_clear_missed_interrupts(fd), 0);
> >
> > - *out = count;
> > + *count = total;
> > return elapsed(&start, &now);
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