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

Umesh Nerlige Ramappa
2023-05-06T00:58:23Z

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;
+
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