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

From: Chris Wilson <chris@chris-wilson.co.uk>
To: "Ville Syrjälä" <ville.syrjala@linux.intel.com>,
	"Tvrtko Ursulin" <tursulin@ursulin.net>,
	"Tvrtko Ursulin" <tvrtko.ursulin@linux.intel.com>
Cc: igt-dev@lists.freedesktop.org, Intel-gfx@lists.freedesktop.org
Subject: Re: [igt-dev] [PATH i-g-t 04/13] gem_wsim: Check sleep times
Date: Fri, 07 Sep 2018 09:45:14 +0100	[thread overview]
Message-ID: <153630991479.16893.7615465871101432757@skylake-alporthouse-com> (raw)
In-Reply-To: <f6e5372c-7f1b-4c45-596f-542c1f9d8e8f@linux.intel.com>

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
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