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

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

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.

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
>