drm/i915/pmu: Add reference counting to the sampling timer

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@intel.com>
Reviewed-by: Umesh Nerlige Ramappa <umesh.nerlige.ramappa@intel.com>
Signed-off-by: Umesh Nerlige Ramappa <umesh.nerlige.ramappa@intel.com>
Reviewed-by: Ashutosh Dixit <ashutosh.dixit@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230519154946.3751971-6-umesh.nerlige.ramappa@intel.com

diff --git a/drivers/gpu/drm/i915/i915_pmu.c b/drivers/gpu/drm/i915/i915_pmu.c
index 890693f..ecb57a9 100644 (file)
--- 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 a686fd7..3a81126 100644 (file)
--- a/drivers/gpu/drm/i915/i915_pmu.h
+++ b/drivers/gpu/drm/i915/i915_pmu.h
@@ -77,6 +77,10 @@ struct i915_pmu {
         */
        spinlock_t lock;
        /**
+        * @unparked: GT unparked mask.
+        */
+       unsigned int unparked;
+       /**
         * @timer: Timer for internal i915 PMU sampling.
         */
        struct hrtimer timer;