Re: [Intel-gfx] [PATCH 4/6] drm/i915/pmu: Add reference counting to the sampling timer

["Dixit, Ashutosh" <ashutosh.dixit@intel.com>]

On Fri, 12 May 2023 15:44:00 -0700, Umesh Nerlige Ramappa wrote:
>
> On Fri, May 12, 2023 at 03:29:03PM -0700, Dixit, Ashutosh wrote:
> > On Fri, 05 May 2023 17:58:14 -0700, Umesh Nerlige Ramappa wrote:
> >>
> >
> > Hi Umesh/Tvrtko,
> >
> >> From: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> >>
> >> We do not want to have timers per tile and waste CPU cycles and energy via
> >> multiple wake-up sources, for a relatively un-important task of PMU
> >> sampling, so keeping a single timer works well. But we also do not want
> >> the first GT which goes idle to turn off the timer.
> >>
> >> Add some reference counting, via a mask of unparked GTs, to solve this.
> >>
> >> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> >> Signed-off-by: Umesh Nerlige Ramappa <umesh.nerlige.ramappa@intel.com>
> >> ---
> >>  drivers/gpu/drm/i915/i915_pmu.c | 12 ++++++++++--
> >>  drivers/gpu/drm/i915/i915_pmu.h |  4 ++++
> >>  2 files changed, 14 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/drivers/gpu/drm/i915/i915_pmu.c b/drivers/gpu/drm/i915/i915_pmu.c
> >> index 2b63ee31e1b3..669a42e44082 100644
> >> --- a/drivers/gpu/drm/i915/i915_pmu.c
> >> +++ b/drivers/gpu/drm/i915/i915_pmu.c
> >> @@ -251,7 +251,9 @@ void i915_pmu_gt_parked(struct intel_gt *gt)
> >>	 * Signal sampling timer to stop if only engine events are enabled and
> >>	 * GPU went idle.
> >>	 */
> >> -	pmu->timer_enabled = pmu_needs_timer(pmu, false);
> >> +	pmu->unparked &= ~BIT(gt->info.id);
> >> +	if (pmu->unparked == 0)
> >> +		pmu->timer_enabled = pmu_needs_timer(pmu, false);
> >>
> >>	spin_unlock_irq(&pmu->lock);
> >>  }
> >> @@ -268,7 +270,10 @@ void i915_pmu_gt_unparked(struct intel_gt *gt)
> >>	/*
> >>	 * Re-enable sampling timer when GPU goes active.
> >>	 */
> >> -	__i915_pmu_maybe_start_timer(pmu);
> >> +	if (pmu->unparked == 0)
> >> +		__i915_pmu_maybe_start_timer(pmu);
> >> +
> >> +	pmu->unparked |= BIT(gt->info.id);
> >>
> >>	spin_unlock_irq(&pmu->lock);
> >>  }
> >> @@ -438,6 +443,9 @@ static enum hrtimer_restart i915_sample(struct hrtimer *hrtimer)
> >>	 */
> >>
> >>	for_each_gt(gt, i915, i) {
> >> +		if (!(pmu->unparked & BIT(i)))
> >> +			continue;
> >> +
> >
> > This is not correct. In this series we are at least sampling frequencies
> > (calling frequency_sample) even when GT is parked. So these 3 lines should be
> > deleted. engines_sample will get called and will return without doing
> > anything if engine events are disabled.
>
> Not sure I understand. This is checking pmu->'un'parked bits.

Sorry, my bad. Not "engines_sample will get called and will return without
doing anything if engine events are disabled" but "engines_sample will get
called and will return without doing anything if GT is not awake". This is
the same as the previous behavior before this series.

Umesh and I discussed this but writing this out in case Tvrtko takes a
look.

Thanks.
--
Ashutosh



> >
> >
> >>		engines_sample(gt, period_ns);
> >>
> >>		if (i == 0) /* FIXME */
> >> diff --git a/drivers/gpu/drm/i915/i915_pmu.h b/drivers/gpu/drm/i915/i915_pmu.h
> >> index a686fd7ccedf..3a811266ac6a 100644
> >> --- a/drivers/gpu/drm/i915/i915_pmu.h
> >> +++ b/drivers/gpu/drm/i915/i915_pmu.h
> >> @@ -76,6 +76,10 @@ struct i915_pmu {
> >>	 * @lock: Lock protecting enable mask and ref count handling.
> >>	 */
> >>	spinlock_t lock;
> >> +	/**
> >> +	 * @unparked: GT unparked mask.
> >> +	 */
> >> +	unsigned int unparked;
> >>	/**
> >>	 * @timer: Timer for internal i915 PMU sampling.
> >>	 */
> >> --
> >> 2.36.1
> >>