[Intel-gfx] [PATCH 1/5] drm/i915/selftests: Skip unstable timing measurements

[Andi Shyti]

Hi Chris,

> > > > > diff --git a/drivers/gpu/drm/i915/selftests/intel_memory_region.c b/drivers/gpu/drm/i915/selftests/intel_memory_region.c
> > > > > index 75839db63bea..59c58a276677 100644
> > > > > --- a/drivers/gpu/drm/i915/selftests/intel_memory_region.c
> > > > > +++ b/drivers/gpu/drm/i915/selftests/intel_memory_region.c
> > > > > @@ -852,6 +852,9 @@ static int _perf_memcpy(struct intel_memory_region *src_mr,
> > > > >               }
> > > > >  
> > > > >               sort(t, ARRAY_SIZE(t), sizeof(*t), wrap_ktime_compare, NULL);
> > > > > +             if (!t[0])
> > > > > +                     continue;
> > > > > +
> > > > 
> > > > are you assuming here that if t[0] is '0', also the rest of 't'
> > > > is '0'?
> > > 
> > > It's sorted into ascending order with ktime_t... Hmm, s64 not u64 as I
> > > presumed. So better to check <= 0.
> > 
> > by division by 0 I guess you mean here:
> > 
> >         div64_u64(mul_u32_u32(4 * size,
> >                               1000 * 1000 * 1000),
> >                   t[1] + 2 * t[2] + t[3]) >> 20);
> > 
> > why are you testing t[0]? Did I miss anything else?
> 
> Since t[0] is the most negative value, if it is <= 0 that implies at
> least one of the measurements was bad. If any are bad, all are bad by
> association. I considered checking t[4] to make sure that at least the
> best was good enough, but paranoia won.

yes, that's what I actually meant with the first question.

Thanks,
Andi