drm/i915: Use spinlocks for checking when to waitboost

In commit 1854d5ca
Author: Chris Wilson <chris@chris-wilson.co.uk>
Date:   Tue Apr 7 16:20:32 2015 +0100

    drm/i915: Deminish contribution of wait-boosting from clients

we removed an atomic timer based check for allowing waitboosting and
moved it below the mutex taken during RPS. However, that mutex can be
held for long periods of time on Vallyview/Cherryview as communication
with the PCU is slow. As clients may frequently wait for results (e.g.
such as tranform feedback) we introduced contention between the client
and the RPS worker. We can take advantage of the RPS worker, by
switching the wait boost decision to use spin locks and defer the
actual reclocking to the worker.

Fixes a regression of up to 45% on Baytrail and Baswell!

v2 (Daniel):
- Use max_freq_softlimit instead of the not-yet-merged boost
  frequency.
- Don't inject a fake irq into the boost work, instead treat
  client_boost as just another legit waker.

v3: Drop the now unused mask (Chris).

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=90112
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> (v1)
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_debugfs.c

@@ -2300,15 +2300,6 @@ static int i915_rps_boost_info(struct seq_file *m, void *data)
 	struct drm_device *dev = node->minor->dev;
 	struct drm_i915_private *dev_priv = dev->dev_private;
 	struct drm_file *file;
-	int ret;
-
-	ret = mutex_lock_interruptible(&dev->struct_mutex);
-	if (ret)
-		return ret;
-
-	ret = mutex_lock_interruptible(&dev_priv->rps.hw_lock);
-	if (ret)
-		goto unlock;
 
 	seq_printf(m, "RPS enabled? %d\n", dev_priv->rps.enabled);
 	seq_printf(m, "GPU busy? %d\n", dev_priv->mm.busy);
@@ -2319,6 +2310,7 @@ static int i915_rps_boost_info(struct seq_file *m, void *data)
 		   intel_gpu_freq(dev_priv, dev_priv->rps.min_freq_softlimit),
 		   intel_gpu_freq(dev_priv, dev_priv->rps.max_freq_softlimit),
 		   intel_gpu_freq(dev_priv, dev_priv->rps.max_freq));
+	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;
@@ -2339,12 +2331,9 @@ static int i915_rps_boost_info(struct seq_file *m, void *data)
 		   dev_priv->rps.mmioflips.boosts,
 		   list_empty(&dev_priv->rps.mmioflips.link) ? "" : ", active");
 	seq_printf(m, "Kernel boosts: %d\n", dev_priv->rps.boosts);
+	spin_unlock(&dev_priv->rps.client_lock);
 
-	mutex_unlock(&dev_priv->rps.hw_lock);
-unlock:
-	mutex_unlock(&dev->struct_mutex);
-
-	return ret;
+	return 0;
 }
 
 static int i915_llc(struct seq_file *m, void *data)

drivers/gpu/drm/i915/i915_drv.h

@@ -1089,9 +1089,12 @@ 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 delayed_resume_work;
-	struct list_head clients;
 	unsigned boosts;
 
 	struct intel_rps_client semaphores, mmioflips;
@@ -1101,7 +1104,9 @@ struct intel_gen6_power_mgmt {
 
 	/*
 	 * Protects RPS/RC6 register access and PCU communication.
-	 * Must be taken after struct_mutex if nested.
+	 * Must be taken after struct_mutex if nested. Note that
+	 * this lock may be held for long periods of time when
+	 * talking to hw - so only take it when talking to hw!
 	 */
 	struct mutex hw_lock;
 };

drivers/gpu/drm/i915/i915_gem.c

@@ -5223,9 +5223,9 @@ void i915_gem_release(struct drm_device *dev, struct drm_file *file)
 	spin_unlock(&file_priv->mm.lock);
 
 	if (!list_empty(&file_priv->rps.link)) {
-		mutex_lock(&to_i915(dev)->rps.hw_lock);
+		spin_lock(&to_i915(dev)->rps.client_lock);
 		list_del(&file_priv->rps.link);
-		mutex_unlock(&to_i915(dev)->rps.hw_lock);
+		spin_unlock(&to_i915(dev)->rps.client_lock);
 	}
 }
 

drivers/gpu/drm/i915/i915_irq.c

@@ -1086,8 +1086,9 @@ static void gen6_pm_rps_work(struct work_struct *work)
 {
 	struct drm_i915_private *dev_priv =
 		container_of(work, struct drm_i915_private, rps.work);
+	bool client_boost;
+	int new_delay, adj, min, max;
 	u32 pm_iir;
-	int new_delay, adj;
 
 	spin_lock_irq(&dev_priv->irq_lock);
 	/* Speed up work cancelation during disabling rps interrupts. */
@@ -1099,12 +1100,14 @@ static void gen6_pm_rps_work(struct work_struct *work)
 	dev_priv->rps.pm_iir = 0;
 	/* Make sure not to corrupt PMIMR state used by ringbuffer on GEN6 */
 	gen6_enable_pm_irq(dev_priv, dev_priv->pm_rps_events);
+	client_boost = dev_priv->rps.client_boost;
+	dev_priv->rps.client_boost = false;
 	spin_unlock_irq(&dev_priv->irq_lock);
 
 	/* Make sure we didn't queue anything we're not going to process. */
 	WARN_ON(pm_iir & ~dev_priv->pm_rps_events);
 
-	if ((pm_iir & dev_priv->pm_rps_events) == 0)
+	if ((pm_iir & dev_priv->pm_rps_events) == 0 && !client_boost)
 		return;
 
 	mutex_lock(&dev_priv->rps.hw_lock);
@@ -1113,7 +1116,13 @@ static void gen6_pm_rps_work(struct work_struct *work)
 
 	adj = dev_priv->rps.last_adj;
 	new_delay = dev_priv->rps.cur_freq;
-	if (pm_iir & GEN6_PM_RP_UP_THRESHOLD) {
+	min = dev_priv->rps.min_freq_softlimit;
+	max = dev_priv->rps.max_freq_softlimit;
+
+	if (client_boost) {
+		new_delay = dev_priv->rps.max_freq_softlimit;
+		adj = 0;
+	} else if (pm_iir & GEN6_PM_RP_UP_THRESHOLD) {
 		if (adj > 0)
 			adj *= 2;
 		else /* CHV needs even encode values */
@@ -1149,9 +1158,7 @@ static void gen6_pm_rps_work(struct work_struct *work)
 	 * interrupt
 	 */
 	new_delay += adj;
-	new_delay = clamp_t(int, new_delay,
-			    dev_priv->rps.min_freq_softlimit,
-			    dev_priv->rps.max_freq_softlimit);
+	new_delay = clamp_t(int, new_delay, min, max);
 
 	intel_set_rps(dev_priv->dev, new_delay);
 

drivers/gpu/drm/i915/intel_pm.c

@@ -4143,17 +4143,25 @@ void gen6_rps_idle(struct drm_i915_private *dev_priv)
 		dev_priv->rps.last_adj = 0;
 		I915_WRITE(GEN6_PMINTRMSK, 0xffffffff);
 	}
+	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);
-	mutex_unlock(&dev_priv->rps.hw_lock);
+	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)
 {
-	u32 val;
+	/* This is intentionally racy! We peek at the state here, then
+	 * validate inside the RPS worker.
+	 */
+	if (!(dev_priv->mm.busy &&
+	      dev_priv->rps.enabled &&
+	      dev_priv->rps.cur_freq < dev_priv->rps.max_freq_softlimit))
+		return;
 
 	/* Force a RPS boost (and don't count it against the client) if
 	 * the GPU is severely congested.
@@ -4161,14 +4169,14 @@ void gen6_rps_boost(struct drm_i915_private *dev_priv,
 	if (rps && time_after(jiffies, submitted + DRM_I915_THROTTLE_JIFFIES))
 		rps = NULL;
 
-	mutex_lock(&dev_priv->rps.hw_lock);
-	val = dev_priv->rps.max_freq_softlimit;
-	if (dev_priv->rps.enabled &&
-	    dev_priv->mm.busy &&
-	    dev_priv->rps.cur_freq < val &&
-	    (rps == NULL || list_empty(&rps->link))) {
-		intel_set_rps(dev_priv->dev, val);
-		dev_priv->rps.last_adj = 0;
+	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;
+			queue_work(dev_priv->wq, &dev_priv->rps.work);
+		}
+		spin_unlock_irq(&dev_priv->irq_lock);
 
 		if (rps != NULL) {
 			list_add(&rps->link, &dev_priv->rps.clients);
@@ -4176,7 +4184,7 @@ void gen6_rps_boost(struct drm_i915_private *dev_priv,
 		} else
 			dev_priv->rps.boosts++;
 	}
-	mutex_unlock(&dev_priv->rps.hw_lock);
+	spin_unlock(&dev_priv->rps.client_lock);
 }
 
 void intel_set_rps(struct drm_device *dev, u8 val)
@@ -6913,6 +6921,7 @@ void intel_pm_setup(struct drm_device *dev)
 	struct drm_i915_private *dev_priv = dev->dev_private;
 
 	mutex_init(&dev_priv->rps.hw_lock);
+	spin_lock_init(&dev_priv->rps.client_lock);
 
 	INIT_DELAYED_WORK(&dev_priv->rps.delayed_resume_work,
 			  intel_gen6_powersave_work);