drm/i915: Avoid keeping waitboost active for signaling threads

Once a client has requested a waitboost, we keep that waitboost active
until all clients are no longer waiting. This is because we don't
distinguish which waiter deserves the boost. However, with the advent of
fence signaling, the signaler threads appear as waiters to the RPS
interrupt handler. So instead of using a single boolean to track when to
keep the waitboost active, use a counter of all outstanding waitboosted
requests.

At this point, I have removed all vestiges of the rate limiting on
clients. Whilst this means that compositors should remain more fluid,
it also means that boosts are more prevalent. See commit b29c19b6
("drm/i915: Boost RPS frequency for CPU stalls") for a longer discussion
on the pros and cons of both approaches.

A drawback of this implementation is that it requires constant request
submission to keep the waitboost trimmed (as it is now cancelled when the
request is completed). This will be fine for a busy system, but near
idle the boosts may be kept for longer than desired (effectively tens of
vblanks worstcase) and there is a reliance on rc6 instead.

v2: Remove defunct rps.client_lock
Reported-by: Michał Winiarski <michal.winiarski@intel.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Michał Winiarski <michal.winiarski@intel.com>
Reviewed-by: Michał Winiarski <michal.winiarski@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170628123548.9236-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_debugfs.c

@@ -2327,6 +2327,8 @@ static int i915_rps_boost_info(struct seq_file *m, void *data)
 	seq_printf(m, "GPU busy? %s [%d requests]\n",
 		   yesno(dev_priv->gt.awake), dev_priv->gt.active_requests);
 	seq_printf(m, "CPU waiting? %d\n", count_irq_waiters(dev_priv));
+	seq_printf(m, "Boosts outstanding? %d\n",
+		   atomic_read(&dev_priv->rps.num_waiters));
 	seq_printf(m, "Frequency requested %d\n",
 		   intel_gpu_freq(dev_priv, dev_priv->rps.cur_freq));
 	seq_printf(m, "  min hard:%d, soft:%d; max soft:%d, hard:%d\n",
@@ -2340,22 +2342,20 @@ static int i915_rps_boost_info(struct seq_file *m, void *data)
 		   intel_gpu_freq(dev_priv, dev_priv->rps.boost_freq));
 
 	mutex_lock(&dev->filelist_mutex);
-	spin_lock(&dev_priv->rps.client_lock);
 	list_for_each_entry_reverse(file, &dev->filelist, lhead) {
 		struct drm_i915_file_private *file_priv = file->driver_priv;
 		struct task_struct *task;
 
 		rcu_read_lock();
 		task = pid_task(file->pid, PIDTYPE_PID);
-		seq_printf(m, "%s [%d]: %d boosts%s\n",
+		seq_printf(m, "%s [%d]: %d boosts\n",
 			   task ? task->comm : "<unknown>",
 			   task ? task->pid : -1,
-			   file_priv->rps.boosts,
-			   list_empty(&file_priv->rps.link) ? "" : ", active");
+			   atomic_read(&file_priv->rps.boosts));
 		rcu_read_unlock();
 	}
-	seq_printf(m, "Kernel (anonymous) boosts: %d\n", dev_priv->rps.boosts);
-	spin_unlock(&dev_priv->rps.client_lock);
+	seq_printf(m, "Kernel (anonymous) boosts: %d\n",
+		   atomic_read(&dev_priv->rps.boosts));
 	mutex_unlock(&dev->filelist_mutex);
 
 	if (INTEL_GEN(dev_priv) >= 6 &&

drivers/gpu/drm/i915/i915_drv.h

@@ -584,8 +584,7 @@ struct drm_i915_file_private {
 	struct idr context_idr;
 
 	struct intel_rps_client {
-		struct list_head link;
-		unsigned boosts;
+		atomic_t boosts;
 	} rps;
 
 	unsigned int bsd_engine;
@@ -1302,13 +1301,10 @@ struct intel_gen6_power_mgmt {
 	int last_adj;
 	enum { LOW_POWER, BETWEEN, HIGH_POWER } power;
 
-	spinlock_t client_lock;
-	struct list_head clients;
-	bool client_boost;
-
 	bool enabled;
 	struct delayed_work autoenable_work;
-	unsigned boosts;
+	atomic_t num_waiters;
+	atomic_t boosts;
 
 	/* manual wa residency calculations */
 	struct intel_rps_ei ei;

drivers/gpu/drm/i915/i915_gem.c

@@ -388,7 +388,7 @@ i915_gem_object_wait_fence(struct dma_fence *fence,
 	 */
 	if (rps) {
 		if (INTEL_GEN(rq->i915) >= 6)
-			gen6_rps_boost(rq->i915, rps, rq->emitted_jiffies);
+			gen6_rps_boost(rq, rps);
 		else
 			rps = NULL;
 	}
@@ -399,22 +399,6 @@ i915_gem_object_wait_fence(struct dma_fence *fence,
 	if (flags & I915_WAIT_LOCKED && i915_gem_request_completed(rq))
 		i915_gem_request_retire_upto(rq);
 
-	if (rps && i915_gem_request_global_seqno(rq) == intel_engine_last_submit(rq->engine)) {
-		/* The GPU is now idle and this client has stalled.
-		 * Since no other client has submitted a request in the
-		 * meantime, assume that this client is the only one
-		 * supplying work to the GPU but is unable to keep that
-		 * work supplied because it is waiting. Since the GPU is
-		 * then never kept fully busy, RPS autoclocking will
-		 * keep the clocks relatively low, causing further delays.
-		 * Compensate by giving the synchronous client credit for
-		 * a waitboost next time.
-		 */
-		spin_lock(&rq->i915->rps.client_lock);
-		list_del_init(&rps->link);
-		spin_unlock(&rq->i915->rps.client_lock);
-	}
-
 	return timeout;
 }
 
@@ -5053,12 +5037,6 @@ void i915_gem_release(struct drm_device *dev, struct drm_file *file)
 	list_for_each_entry(request, &file_priv->mm.request_list, client_link)
 		request->file_priv = NULL;
 	spin_unlock(&file_priv->mm.lock);
-
-	if (!list_empty(&file_priv->rps.link)) {
-		spin_lock(&to_i915(dev)->rps.client_lock);
-		list_del(&file_priv->rps.link);
-		spin_unlock(&to_i915(dev)->rps.client_lock);
-	}
 }
 
 int i915_gem_open(struct drm_i915_private *i915, struct drm_file *file)
@@ -5075,7 +5053,6 @@ int i915_gem_open(struct drm_i915_private *i915, struct drm_file *file)
 	file->driver_priv = file_priv;
 	file_priv->dev_priv = i915;
 	file_priv->file = file;
-	INIT_LIST_HEAD(&file_priv->rps.link);
 
 	spin_lock_init(&file_priv->mm.lock);
 	INIT_LIST_HEAD(&file_priv->mm.request_list);

drivers/gpu/drm/i915/i915_gem_request.c

@@ -384,7 +384,11 @@ static void i915_gem_request_retire(struct drm_i915_gem_request *request)
 		engine->context_unpin(engine, engine->last_retired_context);
 	engine->last_retired_context = request->ctx;
 
-	dma_fence_signal(&request->fence);
+	spin_lock_irq(&request->lock);
+	if (request->waitboost)
+		atomic_dec(&request->i915->rps.num_waiters);
+	dma_fence_signal_locked(&request->fence);
+	spin_unlock_irq(&request->lock);
 
 	i915_priotree_fini(request->i915, &request->priotree);
 	i915_gem_request_put(request);
@@ -639,6 +643,7 @@ i915_gem_request_alloc(struct intel_engine_cs *engine,
 	req->file_priv = NULL;
 	req->batch = NULL;
 	req->capture_list = NULL;
+	req->waitboost = false;
 
 	/*
 	 * Reserve space in the ring buffer for all the commands required to

drivers/gpu/drm/i915/i915_gem_request.h

@@ -184,6 +184,8 @@ struct drm_i915_gem_request {
 	/** Time at which this request was emitted, in jiffies. */
 	unsigned long emitted_jiffies;
 
+	bool waitboost;
+
 	/** engine->request_list entry for this request */
 	struct list_head link;
 

drivers/gpu/drm/i915/i915_irq.c

@@ -1091,18 +1091,6 @@ static u32 vlv_wa_c0_ei(struct drm_i915_private *dev_priv, u32 pm_iir)
 	return events;
 }
 
-static bool any_waiters(struct drm_i915_private *dev_priv)
-{
-	struct intel_engine_cs *engine;
-	enum intel_engine_id id;
-
-	for_each_engine(engine, dev_priv, id)
-		if (intel_engine_has_waiter(engine))
-			return true;
-
-	return false;
-}
-
 static void gen6_pm_rps_work(struct work_struct *work)
 {
 	struct drm_i915_private *dev_priv =
@@ -1114,7 +1102,7 @@ static void gen6_pm_rps_work(struct work_struct *work)
 	spin_lock_irq(&dev_priv->irq_lock);
 	if (dev_priv->rps.interrupts_enabled) {
 		pm_iir = fetch_and_zero(&dev_priv->rps.pm_iir);
-		client_boost = fetch_and_zero(&dev_priv->rps.client_boost);
+		client_boost = atomic_read(&dev_priv->rps.num_waiters);
 	}
 	spin_unlock_irq(&dev_priv->irq_lock);
 
@@ -1131,7 +1119,7 @@ static void gen6_pm_rps_work(struct work_struct *work)
 	new_delay = dev_priv->rps.cur_freq;
 	min = dev_priv->rps.min_freq_softlimit;
 	max = dev_priv->rps.max_freq_softlimit;
-	if (client_boost || any_waiters(dev_priv))
+	if (client_boost)
 		max = dev_priv->rps.max_freq;
 	if (client_boost && new_delay < dev_priv->rps.boost_freq) {
 		new_delay = dev_priv->rps.boost_freq;
@@ -1144,7 +1132,7 @@ static void gen6_pm_rps_work(struct work_struct *work)
 
 		if (new_delay >= dev_priv->rps.max_freq_softlimit)
 			adj = 0;
-	} else if (client_boost || any_waiters(dev_priv)) {
+	} else if (client_boost) {
 		adj = 0;
 	} else if (pm_iir & GEN6_PM_RP_DOWN_TIMEOUT) {
 		if (dev_priv->rps.cur_freq > dev_priv->rps.efficient_freq)

drivers/gpu/drm/i915/intel_drv.h

@@ -1869,9 +1869,8 @@ void intel_suspend_gt_powersave(struct drm_i915_private *dev_priv);
 void gen6_rps_busy(struct drm_i915_private *dev_priv);
 void gen6_rps_reset_ei(struct drm_i915_private *dev_priv);
 void gen6_rps_idle(struct drm_i915_private *dev_priv);
-void gen6_rps_boost(struct drm_i915_private *dev_priv,
-		    struct intel_rps_client *rps,
-		    unsigned long submitted);
+void gen6_rps_boost(struct drm_i915_gem_request *rq,
+		    struct intel_rps_client *rps);
 void intel_queue_rps_boost_for_request(struct drm_i915_gem_request *req);
 void g4x_wm_get_hw_state(struct drm_device *dev);
 void vlv_wm_get_hw_state(struct drm_device *dev);

drivers/gpu/drm/i915/intel_pm.c

@@ -6126,47 +6126,35 @@ void gen6_rps_idle(struct drm_i915_private *dev_priv)
 			   gen6_sanitize_rps_pm_mask(dev_priv, ~0));
 	}
 	mutex_unlock(&dev_priv->rps.hw_lock);
-
-	spin_lock(&dev_priv->rps.client_lock);
-	while (!list_empty(&dev_priv->rps.clients))
-		list_del_init(dev_priv->rps.clients.next);
-	spin_unlock(&dev_priv->rps.client_lock);
 }
 
-void gen6_rps_boost(struct drm_i915_private *dev_priv,
-		    struct intel_rps_client *rps,
-		    unsigned long submitted)
+void gen6_rps_boost(struct drm_i915_gem_request *rq,
+		    struct intel_rps_client *rps)
 {
+	struct drm_i915_private *i915 = rq->i915;
+	bool boost;
+
 	/* This is intentionally racy! We peek at the state here, then
 	 * validate inside the RPS worker.
 	 */
-	if (!(dev_priv->gt.awake &&
-	      dev_priv->rps.enabled &&
-	      dev_priv->rps.cur_freq < dev_priv->rps.boost_freq))
+	if (!i915->rps.enabled)
 		return;
 
-	/* Force a RPS boost (and don't count it against the client) if
-	 * the GPU is severely congested.
-	 */
-	if (rps && time_after(jiffies, submitted + DRM_I915_THROTTLE_JIFFIES))
-		rps = NULL;
-
-	spin_lock(&dev_priv->rps.client_lock);
-	if (rps == NULL || list_empty(&rps->link)) {
-		spin_lock_irq(&dev_priv->irq_lock);
-		if (dev_priv->rps.interrupts_enabled) {
-			dev_priv->rps.client_boost = true;
-			schedule_work(&dev_priv->rps.work);
-		}
-		spin_unlock_irq(&dev_priv->irq_lock);
-
-		if (rps != NULL) {
-			list_add(&rps->link, &dev_priv->rps.clients);
-			rps->boosts++;
-		} else
-			dev_priv->rps.boosts++;
+	boost = false;
+	spin_lock_irq(&rq->lock);
+	if (!rq->waitboost && !i915_gem_request_completed(rq)) {
+		atomic_inc(&i915->rps.num_waiters);
+		rq->waitboost = true;
+		boost = true;
 	}
-	spin_unlock(&dev_priv->rps.client_lock);
+	spin_unlock_irq(&rq->lock);
+	if (!boost)
+		return;
+
+	if (READ_ONCE(i915->rps.cur_freq) < i915->rps.boost_freq)
+		schedule_work(&i915->rps.work);
+
+	atomic_inc(rps ? &rps->boosts : &i915->rps.boosts);
 }
 
 int intel_set_rps(struct drm_i915_private *dev_priv, u8 val)
@@ -9113,7 +9101,7 @@ static void __intel_rps_boost_work(struct work_struct *work)
 	struct drm_i915_gem_request *req = boost->req;
 
 	if (!i915_gem_request_completed(req))
-		gen6_rps_boost(req->i915, NULL, req->emitted_jiffies);
+		gen6_rps_boost(req, NULL);
 
 	i915_gem_request_put(req);
 	kfree(boost);
@@ -9142,11 +9130,10 @@ void intel_queue_rps_boost_for_request(struct drm_i915_gem_request *req)
 void intel_pm_setup(struct drm_i915_private *dev_priv)
 {
 	mutex_init(&dev_priv->rps.hw_lock);
-	spin_lock_init(&dev_priv->rps.client_lock);
 
 	INIT_DELAYED_WORK(&dev_priv->rps.autoenable_work,
 			  __intel_autoenable_gt_powersave);
-	INIT_LIST_HEAD(&dev_priv->rps.clients);
+	atomic_set(&dev_priv->rps.num_waiters, 0);
 
 	dev_priv->pm.suspended = false;
 	atomic_set(&dev_priv->pm.wakeref_count, 0);