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From: Chris Wilson <chris@chris-wilson.co.uk>
To: Mika Kuoppala <mika.kuoppala@linux.intel.com>,
	intel-gfx@lists.freedesktop.org
Subject: Re: [Intel-gfx] [PATCH] drm/i915/selftests: Rearrange ktime_get to reduce latency against CS
Date: Tue, 12 Jan 2021 20:39:40 +0000
Message-ID: <161048398029.9280.6299529944985317684@build.alporthouse.com> (raw)
In-Reply-To: <87im82klo9.fsf@gaia.fi.intel.com>

Quoting Mika Kuoppala (2021-01-12 19:19:34)
> Chris Wilson <chris@chris-wilson.co.uk> writes:
> 
> > In our tests where we measure the elapsed time on both the CPU and CS
> > using a udelay, our CS results match the udelay much more accurately
> > than the ktime (even when using ktime_get_fast_ns). With preemption
> > disabled, we can go one step lower than ktime and use local_clock.
> >
> > Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/2919
> > Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> > ---
> >  drivers/gpu/drm/i915/gt/selftest_engine_pm.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/gt/selftest_engine_pm.c b/drivers/gpu/drm/i915/gt/selftest_engine_pm.c
> > index ca080445695e..c3d965279fc3 100644
> > --- a/drivers/gpu/drm/i915/gt/selftest_engine_pm.c
> > +++ b/drivers/gpu/drm/i915/gt/selftest_engine_pm.c
> > @@ -112,11 +112,11 @@ static int __measure_timestamps(struct intel_context *ce,
> >  
> >       /* Run the request for a 100us, sampling timestamps before/after */
> >       preempt_disable();
> 
> Do you need to promote this to local_irq_disable() ?

Good suggestion. Will try to remember if we still see discrepancies...

Interrupt handlers are meant to <5us, right???
-Chris
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Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-08 10:56 Chris Wilson
2021-01-08 12:46 ` [Intel-gfx] ✓ Fi.CI.BAT: success for " Patchwork
2021-01-08 15:32 ` [Intel-gfx] ✗ Fi.CI.IGT: failure " Patchwork
2021-01-12 19:19 ` [Intel-gfx] [PATCH] " Mika Kuoppala
2021-01-12 20:39   ` Chris Wilson [this message]
2021-01-13 10:52     ` Mika Kuoppala

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