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

[Umesh Nerlige Ramappa]

From: Tvrtko Ursulin <tvrtko.ursu...@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)

Signed-off-by: Tvrtko Ursulin <tvrtko.ursu...@intel.com>
Reviewed-by: Umesh Nerlige Ramappa <umesh.nerlige.rama...@intel.com>
Signed-off-by: Umesh Nerlige Ramappa <umesh.nerlige.rama...@intel.com>
---
 drivers/gpu/drm/i915/i915_pmu.c | 9 +++++++--
 drivers/gpu/drm/i915/i915_pmu.h | 4 ++++
 2 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_pmu.c b/drivers/gpu/drm/i915/i915_pmu.c
index 2b63ee31e1b3..725b01b00775 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);
 }
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