[RFC 14/14] drm/i915/pmu: Wire up engine busy stats to PMU

[Tvrtko Ursulin <tursulin@ursulin.net>]

From: Tvrtko Ursulin <tvrtko.ursulin@intel.com>

We can use engine busy stats instead of the MMIO sampling timer
for better efficiency.

As minimum this saves period * num_engines / sec mmio reads,
and in a better case, when only engine busy samplers are active,
it enables us to not kick off the sampling timer at all.

It is also more accurate since it doesn't rely on sampling.

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
---
 drivers/gpu/drm/i915/i915_drv.h |  3 ++
 drivers/gpu/drm/i915/i915_pmu.c | 64 +++++++++++++++++++++++++++++++++++++----
 2 files changed, 61 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index f1fded6dd9cf..2986a01660d8 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -2603,8 +2603,11 @@ struct drm_i915_private {
 		spinlock_t lock;
 		struct hrtimer timer;
 		bool timer_enabled;
+		bool busy_stats;
 		u64 enable;
 		u64 sample[__I915_NUM_PMU_SAMPLERS];
+		struct work_struct enable_busy_stats;
+		struct delayed_work disable_busy_stats;
 	} pmu;
 
 	/*
diff --git a/drivers/gpu/drm/i915/i915_pmu.c b/drivers/gpu/drm/i915/i915_pmu.c
index 4b113cad40d1..996612843594 100644
--- a/drivers/gpu/drm/i915/i915_pmu.c
+++ b/drivers/gpu/drm/i915/i915_pmu.c
@@ -29,12 +29,23 @@ static const unsigned int user_engine_map[I915_NUM_ENGINES] = {
 	[I915_SAMPLE_VECS] = VECS,
 };
 
+#define ENGINE_BUSY_BITS \
+	(BIT_ULL(I915_PMU_COUNT_RCS_BUSY) | \
+	 BIT_ULL(I915_PMU_COUNT_BCS_BUSY) | \
+	 BIT_ULL(I915_PMU_COUNT_VCS_BUSY) | \
+	 BIT_ULL(I915_PMU_COUNT_VCS2_BUSY) | \
+	 BIT_ULL(I915_PMU_COUNT_VECS_BUSY))
+
 static bool pmu_needs_timer(struct drm_i915_private *i915, bool gpu_active)
 {
-	if (gpu_active)
-		return i915->pmu.enable;
-	else
-		return i915->pmu.enable >> 32;
+	u64 mask = i915->pmu.enable;
+
+	if (!gpu_active)
+		mask >>= 32;
+	else if (i915->pmu.busy_stats)
+		mask &= ~ENGINE_BUSY_BITS;
+
+	return mask;
 }
 
 void i915_pmu_gt_idle(struct drm_i915_private *i915)
@@ -110,7 +121,8 @@ static void engines_sample(struct drm_i915_private *dev_priv)
 		if (sample_mask & BIT(I915_SAMPLE_QUEUED))
 			engine->pmu_sample[I915_SAMPLE_QUEUED] += PERIOD;
 
-		if (sample_mask & BIT(I915_SAMPLE_BUSY)) {
+		if ((sample_mask & BIT(I915_SAMPLE_BUSY)) &&
+		    !dev_priv->pmu.busy_stats) {
 			fw = grab_forcewake(dev_priv, fw);
 			val = I915_READ_FW(RING_MI_MODE(engine->mmio_base));
 			if (!(val & MODE_IDLE))
@@ -337,6 +349,11 @@ static void i915_pmu_timer_cancel(struct perf_event *event)
 	hrtimer_cancel(&hwc->hrtimer);
 }
 
+static bool supports_busy_stats(void)
+{
+	return i915.enable_execlists;
+}
+
 static void i915_pmu_enable(struct perf_event *event)
 {
 	struct drm_i915_private *i915 =
@@ -345,6 +362,13 @@ static void i915_pmu_enable(struct perf_event *event)
 
 	spin_lock_irqsave(&i915->pmu.lock, flags);
 
+	if (pmu_config_sampler(event->attr.config) == I915_SAMPLE_BUSY &&
+	    supports_busy_stats() && !i915->pmu.busy_stats) {
+		i915->pmu.busy_stats = true;
+		if (!cancel_delayed_work(&i915->pmu.disable_busy_stats))
+			queue_work(i915->wq, &i915->pmu.enable_busy_stats);
+	}
+
 	i915->pmu.enable |= BIT_ULL(event->attr.config);
 	if (pmu_needs_timer(i915, true) && !i915->pmu.timer_enabled) {
 		hrtimer_start_range_ns(&i915->pmu.timer,
@@ -367,6 +391,11 @@ static void i915_pmu_disable(struct perf_event *event)
 	spin_lock_irqsave(&i915->pmu.lock, flags);
 	i915->pmu.enable &= ~BIT_ULL(event->attr.config);
 	i915->pmu.timer_enabled &= pmu_needs_timer(i915, true);
+	if (!(i915->pmu.enable & ENGINE_BUSY_BITS) && i915->pmu.busy_stats) {
+		i915->pmu.busy_stats = false;
+		queue_delayed_work(i915->wq, &i915->pmu.disable_busy_stats,
+				   round_jiffies_up_relative(2 * HZ));
+	}
 	spin_unlock_irqrestore(&i915->pmu.lock, flags);
 
 	i915_pmu_timer_cancel(event);
@@ -471,7 +500,12 @@ static void i915_pmu_event_read(struct perf_event *event)
 			/* Do nothing */
 		} else {
 			enum intel_engine_id id = user_engine_map[user_engine];
-			val = i915->engine[id]->pmu_sample[sample];
+			struct intel_engine_cs *engine = i915->engine[id];
+
+			if (i915->pmu.busy_stats && sample == I915_SAMPLE_BUSY)
+				val = intel_engine_get_current_busy_ns(engine);
+			else
+				val = engine->pmu_sample[sample];
 		}
 	} else switch (event->attr.config) {
 	case I915_PMU_ACTUAL_FREQUENCY:
@@ -607,6 +641,19 @@ static const struct attribute_group *i915_pmu_attr_groups[] = {
         NULL
 };
 
+static void __enable_busy_stats(struct work_struct *work)
+{
+	struct drm_i915_private *i915 =
+		container_of(work, typeof(*i915), pmu.enable_busy_stats);
+
+	WARN_ON_ONCE(intel_enable_engine_stats(i915));
+}
+
+static void __disable_busy_stats(struct work_struct *work)
+{
+	intel_disable_engine_stats();
+}
+
 void i915_pmu_register(struct drm_i915_private *i915)
 {
 	if (INTEL_GEN(i915) <= 2)
@@ -624,6 +671,8 @@ void i915_pmu_register(struct drm_i915_private *i915)
 
 	spin_lock_init(&i915->pmu.lock);
 	hrtimer_init(&i915->pmu.timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
+	INIT_WORK(&i915->pmu.enable_busy_stats, __enable_busy_stats);
+	INIT_DELAYED_WORK(&i915->pmu.disable_busy_stats, __disable_busy_stats);
 	i915->pmu.timer.function = i915_sample;
 	i915->pmu.enable = 0;
 
@@ -642,4 +691,7 @@ void i915_pmu_unregister(struct drm_i915_private *i915)
 	i915->pmu.base.event_init = NULL;
 
 	hrtimer_cancel(&i915->pmu.timer);
+
+	flush_work(&i915->pmu.enable_busy_stats);
+	flush_delayed_work(&i915->pmu.disable_busy_stats);
 }
-- 
2.9.4

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