drm/i915/gt: Always enable busy-stats for execlists

In the near future, we will utilize the busy-stats on each engine to
approximate the C0 cycles of each, and use that as an input to a manual
RPS mechanism. That entails having busy-stats always enabled and so we
can remove the enable/disable routines and simplify the pmu setup. As a
consequence of always having the stats enabled, we can also show the
current active time via sysfs/engine/xcs/active_time_ns.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200429205446.3259-1-chris@chris-wilson.co.uk

4 files changed, 24 insertions, 128 deletions

diff --git a/drivers/gpu/drm/i915/gt/intel_engine.h b/drivers/gpu/drm/i915/gt/intel_engine.h
index d9ee64e2ef79..d10e52ff059f 100644
--- a/drivers/gpu/drm/i915/gt/intel_engine.h
+++ b/drivers/gpu/drm/i915/gt/intel_engine.h
@@ -310,9 +310,6 @@ void intel_engine_dump(struct intel_engine_cs *engine,
 		       struct drm_printer *m,
 		       const char *header, ...);
 
-int intel_enable_engine_stats(struct intel_engine_cs *engine);
-void intel_disable_engine_stats(struct intel_engine_cs *engine);
-
 ktime_t intel_engine_get_busy_time(struct intel_engine_cs *engine);
 
 struct i915_request *
diff --git a/drivers/gpu/drm/i915/gt/intel_engine_cs.c b/drivers/gpu/drm/i915/gt/intel_engine_cs.c
index 80bf71636c0f..c9e46c5ced43 100644
--- a/drivers/gpu/drm/i915/gt/intel_engine_cs.c
+++ b/drivers/gpu/drm/i915/gt/intel_engine_cs.c
@@ -1589,58 +1589,6 @@ void intel_engine_dump(struct intel_engine_cs *engine,
 	intel_engine_print_breadcrumbs(engine, m);
 }
 
-/**
- * intel_enable_engine_stats() - Enable engine busy tracking on engine
- * @engine: engine to enable stats collection
- *
- * Start collecting the engine busyness data for @engine.
- *
- * Returns 0 on success or a negative error code.
- */
-int intel_enable_engine_stats(struct intel_engine_cs *engine)
-{
-	struct intel_engine_execlists *execlists = &engine->execlists;
-	unsigned long flags;
-	int err = 0;
-
-	if (!intel_engine_supports_stats(engine))
-		return -ENODEV;
-
-	execlists_active_lock_bh(execlists);
-	write_seqlock_irqsave(&engine->stats.lock, flags);
-
-	if (unlikely(engine->stats.enabled == ~0)) {
-		err = -EBUSY;
-		goto unlock;
-	}
-
-	if (engine->stats.enabled++ == 0) {
-		struct i915_request * const *port;
-		struct i915_request *rq;
-
-		engine->stats.enabled_at = ktime_get();
-
-		/* XXX submission method oblivious? */
-		for (port = execlists->active; (rq = *port); port++)
-			engine->stats.active++;
-
-		for (port = execlists->pending; (rq = *port); port++) {
-			/* Exclude any contexts already counted in active */
-			if (!intel_context_inflight_count(rq->context))
-				engine->stats.active++;
-		}
-
-		if (engine->stats.active)
-			engine->stats.start = engine->stats.enabled_at;
-	}
-
-unlock:
-	write_sequnlock_irqrestore(&engine->stats.lock, flags);
-	execlists_active_unlock_bh(execlists);
-
-	return err;
-}
-
 static ktime_t __intel_engine_get_busy_time(struct intel_engine_cs *engine)
 {
 	ktime_t total = engine->stats.total;
@@ -1649,7 +1597,7 @@ static ktime_t __intel_engine_get_busy_time(struct intel_engine_cs *engine)
 	 * If the engine is executing something at the moment
 	 * add it to the total.
 	 */
-	if (engine->stats.active)
+	if (atomic_read(&engine->stats.active))
 		total = ktime_add(total,
 				  ktime_sub(ktime_get(), engine->stats.start));
 
@@ -1675,28 +1623,6 @@ ktime_t intel_engine_get_busy_time(struct intel_engine_cs *engine)
 	return total;
 }
 
-/**
- * intel_disable_engine_stats() - Disable engine busy tracking on engine
- * @engine: engine to disable stats collection
- *
- * Stops collecting the engine busyness data for @engine.
- */
-void intel_disable_engine_stats(struct intel_engine_cs *engine)
-{
-	unsigned long flags;
-
-	if (!intel_engine_supports_stats(engine))
-		return;
-
-	write_seqlock_irqsave(&engine->stats.lock, flags);
-	WARN_ON_ONCE(engine->stats.enabled == 0);
-	if (--engine->stats.enabled == 0) {
-		engine->stats.total = __intel_engine_get_busy_time(engine);
-		engine->stats.active = 0;
-	}
-	write_sequnlock_irqrestore(&engine->stats.lock, flags);
-}
-
 static bool match_ring(struct i915_request *rq)
 {
 	u32 ring = ENGINE_READ(rq->engine, RING_START);
diff --git a/drivers/gpu/drm/i915/gt/intel_engine_types.h b/drivers/gpu/drm/i915/gt/intel_engine_types.h
index 483d8ff39a0d..83b1f95ebf12 100644
--- a/drivers/gpu/drm/i915/gt/intel_engine_types.h
+++ b/drivers/gpu/drm/i915/gt/intel_engine_types.h
@@ -532,27 +532,15 @@ struct intel_engine_cs {
 
 	struct {
 		/**
-		 * @lock: Lock protecting the below fields.
-		 */
-		seqlock_t lock;
-		/**
-		 * @enabled: Reference count indicating number of listeners.
-		 */
-		unsigned int enabled;
-		/**
 		 * @active: Number of contexts currently scheduled in.
 		 */
-		unsigned int active;
-		/**
-		 * @enabled_at: Timestamp when busy stats were enabled.
-		 */
-		ktime_t enabled_at;
+		atomic_t active;
+
 		/**
-		 * @start: Timestamp of the last idle to active transition.
-		 *
-		 * Idle is defined as active == 0, active is active > 0.
+		 * @lock: Lock protecting the below fields.
 		 */
-		ktime_t start;
+		seqlock_t lock;
+
 		/**
 		 * @total: Total time this engine was busy.
 		 *
@@ -560,6 +548,13 @@ struct intel_engine_cs {
 		 * where engine is currently busy (active > 0).
 		 */
 		ktime_t total;
+
+		/**
+		 * @start: Timestamp of the last idle to active transition.
+		 *
+		 * Idle is defined as active == 0, active is active > 0.
+		 */
+		ktime_t start;
 	} stats;
 
 	struct {
diff --git a/drivers/gpu/drm/i915/gt/intel_lrc.c b/drivers/gpu/drm/i915/gt/intel_lrc.c
index 7fc4081c34fe..4311b12542fb 100644
--- a/drivers/gpu/drm/i915/gt/intel_lrc.c
+++ b/drivers/gpu/drm/i915/gt/intel_lrc.c
@@ -1199,17 +1199,14 @@ static void intel_engine_context_in(struct intel_engine_cs *engine)
 {
 	unsigned long flags;
 
-	if (READ_ONCE(engine->stats.enabled) == 0)
+	if (atomic_add_unless(&engine->stats.active, 1, 0))
 		return;
 
 	write_seqlock_irqsave(&engine->stats.lock, flags);
-
-	if (engine->stats.enabled > 0) {
-		if (engine->stats.active++ == 0)
-			engine->stats.start = ktime_get();
-		GEM_BUG_ON(engine->stats.active == 0);
+	if (!atomic_add_unless(&engine->stats.active, 1, 0)) {
+		engine->stats.start = ktime_get();
+		atomic_inc(&engine->stats.active);
 	}
-
 	write_sequnlock_irqrestore(&engine->stats.lock, flags);
 }
 
@@ -1217,36 +1214,17 @@ static void intel_engine_context_out(struct intel_engine_cs *engine)
 {
 	unsigned long flags;
 
-	if (READ_ONCE(engine->stats.enabled) == 0)
+	GEM_BUG_ON(!atomic_read(&engine->stats.active));
+
+	if (atomic_add_unless(&engine->stats.active, -1, 1))
 		return;
 
 	write_seqlock_irqsave(&engine->stats.lock, flags);
-
-	if (engine->stats.enabled > 0) {
-		ktime_t last;
-
-		if (engine->stats.active && --engine->stats.active == 0) {
-			/*
-			 * Decrement the active context count and in case GPU
-			 * is now idle add up to the running total.
-			 */
-			last = ktime_sub(ktime_get(), engine->stats.start);
-
-			engine->stats.total = ktime_add(engine->stats.total,
-							last);
-		} else if (engine->stats.active == 0) {
-			/*
-			 * After turning on engine stats, context out might be
-			 * the first event in which case we account from the
-			 * time stats gathering was turned on.
-			 */
-			last = ktime_sub(ktime_get(), engine->stats.enabled_at);
-
-			engine->stats.total = ktime_add(engine->stats.total,
-							last);
-		}
+	if (atomic_dec_and_test(&engine->stats.active)) {
+		engine->stats.total =
+			ktime_add(engine->stats.total,
+				  ktime_sub(ktime_get(), engine->stats.start));
 	}
-
 	write_sequnlock_irqrestore(&engine->stats.lock, flags);
 }