[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)
v3: Remove gpu_active argument of pmu_needs_timer (Andrzej)

Signed-off-by: Ashutosh Dixit <ashutosh.di...@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursu...@intel.com>
---
 drivers/gpu/drm/i915/i915_pmu.c | 16 +++++-----------
 1 file changed, 5 insertions(+), 11 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_pmu.c b/drivers/gpu/drm/i915/i915_pmu.c
index a814583e19fd7..09313cf9316b4 100644
--- a/drivers/gpu/drm/i915/i915_pmu.c
+++ b/drivers/gpu/drm/i915/i915_pmu.c
@@ -139,7 +139,7 @@ static u32 frequency_enabled_mask(void)
        return mask;
 }
 
-static bool pmu_needs_timer(struct i915_pmu *pmu, bool gpu_active)
+static bool pmu_needs_timer(struct i915_pmu *pmu)
 {
        struct drm_i915_private *i915 = container_of(pmu, typeof(*i915), pmu);
        u32 enable;
@@ -157,17 +157,11 @@ 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);
 
        /*
@@ -295,7 +289,7 @@ static void park_rc6(struct intel_gt *gt)
 
 static void __i915_pmu_maybe_start_timer(struct i915_pmu *pmu)
 {
-       if (!pmu->timer_enabled && pmu_needs_timer(pmu, true)) {
+       if (!pmu->timer_enabled && pmu_needs_timer(pmu)) {
                pmu->timer_enabled = true;
                pmu->timer_last = ktime_get();
                hrtimer_start_range_ns(&pmu->timer,
@@ -321,7 +315,7 @@ void i915_pmu_gt_parked(struct intel_gt *gt)
         */
        pmu->unparked &= ~BIT(gt->info.id);
        if (pmu->unparked == 0)
-               pmu->timer_enabled = pmu_needs_timer(pmu, false);
+               pmu->timer_enabled = false;
 
        spin_unlock_irq(&pmu->lock);
 }
@@ -827,7 +821,7 @@ static void i915_pmu_disable(struct perf_event *event)
         */
        if (--pmu->enable_count[bit] == 0) {
                pmu->enable &= ~BIT(bit);
-               pmu->timer_enabled &= pmu_needs_timer(pmu, true);
+               pmu->timer_enabled &= pmu_needs_timer(pmu);
        }
 
        spin_unlock_irqrestore(&pmu->lock, flags);
-- 
2.38.0