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

Umesh Nerlige Ramappa
2023-05-12T22:45:15Z

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.

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
>>