From: Mika Kuoppala <mika.kuoppala@linux.intel.com>
To: Chris Wilson <chris@chris-wilson.co.uk>, intel-gfx@lists.freedesktop.org
Subject: Re: [Intel-gfx] [PATCH] drm/i915/selftests: Rearrange ktime_get to reduce latency against CS
Date: Wed, 13 Jan 2021 12:52:40 +0200 [thread overview]
Message-ID: <87ft35kt1j.fsf@gaia.fi.intel.com> (raw)
In-Reply-To: <161048398029.9280.6299529944985317684@build.alporthouse.com>
Chris Wilson <chris@chris-wilson.co.uk> writes:
> 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???
With both test types, we might sometimes find out what they are :)
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
> -Chris
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prev parent reply other threads:[~2021-01-13 10:55 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-08 10:56 [Intel-gfx] [PATCH] drm/i915/selftests: Rearrange ktime_get to reduce latency against CS 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
2021-01-13 10:52 ` Mika Kuoppala [this message]
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