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

[Umesh Nerlige Ramappa <umesh.nerlige.ramappa@intel.com>]

On Fri, May 05, 2023 at 05:58:14PM -0700, Umesh Nerlige Ramappa wrote:
>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.

Looks like the previous patch is a prep work for this one. I would 
mention something about this patch in the previous patch, but then I am 
not sure what's the norm in these scenarios. Recently I created some IGT 
patches that are prep work and refer to future patches in the series.

As is, this patch is 

Reviewed-by: Umesh Nerlige Ramappa <umesh.nerlige.ramappa@intel.com>

Thanks,
Umesh

>
>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;
>+
> 		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
>