[Intel-gfx] [PATCH 1/2] drm/i915/pmu: Turn off the timer to sample frequencies when GT is parked

[Ashutosh Dixit]

pmu_needs_timer() keeps the timer running even when GT is parked,
ostensibly to sample requested/actual frequencies. However
frequency_sample() has the following:

	/* Report 0/0 (actual/requested) frequency while parked. */
	if (!intel_gt_pm_get_if_awake(gt))
		return;

The above code prevents frequencies to be sampled while the GT is
parked. So we might as well turn off the sampling timer itself in this
case and save CPU cycles/power.

v2: Instead of turning freq bits off, return false, since no counters will
    run after this change when GT is parked (Tvrtko)

Signed-off-by: Ashutosh Dixit <ashutosh.dixit at intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
---
 drivers/gpu/drm/i915/i915_pmu.c | 12 +++++-------
 1 file changed, 5 insertions(+), 7 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_pmu.c b/drivers/gpu/drm/i915/i915_pmu.c
index a814583e19fd7..b47d890d4ada1 100644
--- a/drivers/gpu/drm/i915/i915_pmu.c
+++ b/drivers/gpu/drm/i915/i915_pmu.c
@@ -144,6 +144,10 @@ static bool pmu_needs_timer(struct i915_pmu *pmu, bool gpu_active)
 	struct drm_i915_private *i915 = container_of(pmu, typeof(*i915), pmu);
 	u32 enable;
 
+	/* When GPU is idle, at present no counters need to run */
+	if (!gpu_active)
+		return false;
+
 	/*
 	 * Only some counters need the sampling timer.
 	 *
@@ -157,17 +161,11 @@ static bool pmu_needs_timer(struct i915_pmu *pmu, bool gpu_active)
 	 */
 	enable &= frequency_enabled_mask() | ENGINE_SAMPLE_MASK;
 
-	/*
-	 * When the GPU is idle per-engine counters do not need to be
-	 * running so clear those bits out.
-	 */
-	if (!gpu_active)
-		enable &= ~ENGINE_SAMPLE_MASK;
 	/*
 	 * Also there is software busyness tracking available we do not
 	 * need the timer for I915_SAMPLE_BUSY counter.
 	 */
-	else if (i915->caps.scheduler & I915_SCHEDULER_CAP_ENGINE_BUSY_STATS)
+	if (i915->caps.scheduler & I915_SCHEDULER_CAP_ENGINE_BUSY_STATS)
 		enable &= ~BIT(I915_SAMPLE_BUSY);
 
 	/*
-- 
2.38.0