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

Umesh Nerlige Ramappa
2023-05-12T23:44:44Z

On Fri, May 12, 2023 at 04:20:19PM -0700, Dixit, Ashutosh wrote:
>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.

Sounds good, Dropping the check here in the new revision.

Thanks,
Umesh
>
>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
>> >>