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

From: Andi Shyti <andi@etezian.org>
To: Chris Wilson <chris@chris-wilson.co.uk>
Cc: intel-gfx@lists.freedesktop.org
Subject: Re: [Intel-gfx] [PATCH 1/5] drm/i915/selftests: Skip unstable timing measurements
Date: Fri, 8 Jan 2021 15:51:54 +0200	[thread overview]
Message-ID: <X/hjekGVV5F+sokg@jack.zhora.eu> (raw)
In-Reply-To: <161011238272.28368.13711350036924329757@build.alporthouse.com>

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?

Andi
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