Re: [igt-dev] [PATH i-g-t 04/13] gem_wsim: Check sleep times

Chris Wilson
2018-09-07T08:45:14Z

Quoting Tvrtko Ursulin (2018-09-07 09:37:00)
>
> On 05/09/2018 15:09, Ville Syrjälä wrote:
> > On Wed, Sep 05, 2018 at 02:49:30PM +0100, Tvrtko Ursulin wrote:
> >> From: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> >>
> >> Notice in more places if we are running behind.
> >>
> >> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> >> ---
> >> benchmarks/gem_wsim.c | 52 ++++++++++++++++++++++++++++++++++++++-----
> >> 1 file changed, 46 insertions(+), 6 deletions(-)
> >>
> >> diff --git a/benchmarks/gem_wsim.c b/benchmarks/gem_wsim.c
> >> index 25af4d678ba4..b05e9760f419 100644
> >> --- a/benchmarks/gem_wsim.c
> >> +++ b/benchmarks/gem_wsim.c
> >> @@ -1718,6 +1718,21 @@ static bool sync_deps(struct workload *wrk, struct w_step *w)
> >> return synced;
> >> }
> >>
> >> +static unsigned int measured_usleep(unsigned int usec)
> >> +{
> >> + struct timespec ts = { };
> >> + unsigned int slept;
> >> +
> >> + slept = igt_nsec_elapsed(&ts);
> >> + igt_assert(slept == 0);
> >> + do {
> >> + usleep(usec - slept);
> >> + slept = igt_nsec_elapsed(&ts) / 1000;
> >> + } while (slept < usec);
> >
> > clock_nanosleep(ABS)?
>
> Hm I think I see what you mean. Rather than a relative sleep trying to
> hit the loop period, ask from the kernel (or glibc, I don't know who
> implements it) to sleep until an absolute target. This totally makes
> sense and would simplify the code from one angle, I am just not sure if
> absolute sleep can be relied upon any better to not oversleep. Well,
> actually for scheduling delays not to affect the caller. However maybe
> it doesn't matter since AFAIR my main problem were dropped period due
> GPU activity (the first pair of warning messages in the patch), and
> again AFAIR, it was quite hard to hit the second ones.

Right, it removes the loop but we still want to keep the measurement.
-Chris