[Intel-gfx] [PATCH v5 5/7] drm/i915/pmu: Add reference counting to the sampling timer

[Umesh Nerlige Ramappa]

From: Tvrtko Ursulin <tvrtko.ursulin at 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.

v2: Drop the check for unparked in i915_sample (Ashutosh)
v3: Revert v2 (Tvrtko)

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
Reviewed-by: Umesh Nerlige Ramappa <umesh.nerlige.ramappa at intel.com>
Signed-off-by: Umesh Nerlige Ramappa <umesh.nerlige.ramappa at intel.com>
Reviewed-by: Ashutosh Dixit <ashutosh.dixit at 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 890693fdaf9e..ecb57a94143e 100644
--- a/drivers/gpu/drm/i915/i915_pmu.c
+++ b/drivers/gpu/drm/i915/i915_pmu.c
@@ -262,7 +262,9 @@ 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);
 }
@@ -279,7 +281,10 @@ 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);
 }
@@ -449,6 +454,9 @@ 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