drm/i915: Only start retire worker when idle

The retire worker is a low frequency task that makes sure we retire
outstanding requests if userspace is being lax. We only need to start it
once as it remains active until the GPU is idle, so do a cheap test
before the more expensive queue_work(). A consequence of this is that we
need correct locking in the worker to make the hot path of request
submission cheap. To keep the symmetry and keep hangcheck strictly bound
by the GPU's wakelock, we move the cancel_sync(hangcheck) to the idle
worker before dropping the wakelock.

v2: Guard against RCU fouling the breadcrumbs bottom-half whilst we kick
the waiter.
v3: Remove the wakeref assertion squelching (now we hold a wakeref for
the hangcheck, any rpm error there is genuine).
v4: To prevent excess work when retiring requests, we split the busy
flag into two, a boolean to denote whether we hold the wakeref and a
bitmask of active engines.
v5: Reorder cancelling hangcheck upon idling to avoid a race where we
might cancel a hangcheck after being preempted by a new task

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
References: https://bugs.freedesktop.org/show_bug.cgi?id=88437
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1467616119-4093-1-git-send-email-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_debugfs.c

@@ -2442,7 +2442,8 @@ static int i915_rps_boost_info(struct seq_file *m, void *data)
 	struct drm_file *file;
 
 	seq_printf(m, "RPS enabled? %d\n", dev_priv->rps.enabled);
-	seq_printf(m, "GPU busy? %d\n", dev_priv->mm.busy);
+	seq_printf(m, "GPU busy? %s [%x]\n",
+		   yesno(dev_priv->gt.awake), dev_priv->gt.active_engines);
 	seq_printf(m, "CPU waiting? %d\n", count_irq_waiters(dev_priv));
 	seq_printf(m, "Frequency requested %d; min hard:%d, soft:%d; max soft:%d, hard:%d\n",
 		   intel_gpu_freq(dev_priv, dev_priv->rps.cur_freq),
@@ -2786,7 +2787,7 @@ static int i915_runtime_pm_status(struct seq_file *m, void *unused)
 	if (!HAS_RUNTIME_PM(dev_priv))
 		seq_puts(m, "Runtime power management not supported\n");
 
-	seq_printf(m, "GPU idle: %s\n", yesno(!dev_priv->mm.busy));
+	seq_printf(m, "GPU idle: %s\n", yesno(!dev_priv->gt.awake));
 	seq_printf(m, "IRQs disabled: %s\n",
 		   yesno(!intel_irqs_enabled(dev_priv)));
 #ifdef CONFIG_PM

drivers/gpu/drm/i915/i915_drv.c

@@ -2735,8 +2735,6 @@ static int intel_runtime_suspend(struct device *device)
 	i915_gem_release_all_mmaps(dev_priv);
 	mutex_unlock(&dev->struct_mutex);
 
-	cancel_delayed_work_sync(&dev_priv->gpu_error.hangcheck_work);
-
 	intel_guc_suspend(dev);
 
 	intel_suspend_gt_powersave(dev_priv);

drivers/gpu/drm/i915/i915_drv.h

@@ -1313,38 +1313,12 @@ struct i915_gem_mm {
 	/** LRU list of objects with fence regs on them. */
 	struct list_head fence_list;
 
-	/**
-	 * We leave the user IRQ off as much as possible,
-	 * but this means that requests will finish and never
-	 * be retired once the system goes idle. Set a timer to
-	 * fire periodically while the ring is running. When it
-	 * fires, go retire requests.
-	 */
-	struct delayed_work retire_work;
-
-	/**
-	 * When we detect an idle GPU, we want to turn on
-	 * powersaving features. So once we see that there
-	 * are no more requests outstanding and no more
-	 * arrive within a small period of time, we fire
-	 * off the idle_work.
-	 */
-	struct delayed_work idle_work;
-
 	/**
 	 * Are we in a non-interruptible section of code like
 	 * modesetting?
 	 */
 	bool interruptible;
 
-	/**
-	 * Is the GPU currently considered idle, or busy executing userspace
-	 * requests?  Whilst idle, we attempt to power down the hardware and
-	 * display clocks. In order to reduce the effect on performance, there
-	 * is a slight delay before we do so.
-	 */
-	bool busy;
-
 	/* the indicator for dispatch video commands on two BSD rings */
 	unsigned int bsd_ring_dispatch_index;
 
@@ -2045,6 +2019,34 @@ struct drm_i915_private {
 		int (*init_engines)(struct drm_device *dev);
 		void (*cleanup_engine)(struct intel_engine_cs *engine);
 		void (*stop_engine)(struct intel_engine_cs *engine);
+
+		/**
+		 * Is the GPU currently considered idle, or busy executing
+		 * userspace requests? Whilst idle, we allow runtime power
+		 * management to power down the hardware and display clocks.
+		 * In order to reduce the effect on performance, there
+		 * is a slight delay before we do so.
+		 */
+		unsigned int active_engines;
+		bool awake;
+
+		/**
+		 * We leave the user IRQ off as much as possible,
+		 * but this means that requests will finish and never
+		 * be retired once the system goes idle. Set a timer to
+		 * fire periodically while the ring is running. When it
+		 * fires, go retire requests.
+		 */
+		struct delayed_work retire_work;
+
+		/**
+		 * When we detect an idle GPU, we want to turn on
+		 * powersaving features. So once we see that there
+		 * are no more requests outstanding and no more
+		 * arrive within a small period of time, we fire
+		 * off the idle_work.
+		 */
+		struct delayed_work idle_work;
 	} gt;
 
 	/* perform PHY state sanity checks? */
@@ -3315,7 +3317,7 @@ int __must_check i915_gem_set_seqno(struct drm_device *dev, u32 seqno);
 struct drm_i915_gem_request *
 i915_gem_find_active_request(struct intel_engine_cs *engine);
 
-bool i915_gem_retire_requests(struct drm_i915_private *dev_priv);
+void i915_gem_retire_requests(struct drm_i915_private *dev_priv);
 void i915_gem_retire_requests_ring(struct intel_engine_cs *engine);
 
 static inline u32 i915_reset_counter(struct i915_gpu_error *error)

drivers/gpu/drm/i915/i915_gem.c

@@ -2809,6 +2809,26 @@ i915_gem_get_seqno(struct drm_i915_private *dev_priv, u32 *seqno)
 	return 0;
 }
 
+static void i915_gem_mark_busy(const struct intel_engine_cs *engine)
+{
+	struct drm_i915_private *dev_priv = engine->i915;
+
+	dev_priv->gt.active_engines |= intel_engine_flag(engine);
+	if (dev_priv->gt.awake)
+		return;
+
+	intel_runtime_pm_get_noresume(dev_priv);
+	dev_priv->gt.awake = true;
+
+	i915_update_gfx_val(dev_priv);
+	if (INTEL_GEN(dev_priv) >= 6)
+		gen6_rps_busy(dev_priv);
+
+	queue_delayed_work(dev_priv->wq,
+			   &dev_priv->gt.retire_work,
+			   round_jiffies_up_relative(HZ));
+}
+
 /*
  * NB: This function is not allowed to fail. Doing so would mean the the
  * request is not being tracked for completion but the work itself is
@@ -2819,7 +2839,6 @@ void __i915_add_request(struct drm_i915_gem_request *request,
 			bool flush_caches)
 {
 	struct intel_engine_cs *engine;
-	struct drm_i915_private *dev_priv;
 	struct intel_ringbuffer *ringbuf;
 	u32 request_start;
 	u32 reserved_tail;
@@ -2829,7 +2848,6 @@ void __i915_add_request(struct drm_i915_gem_request *request,
 		return;
 
 	engine = request->engine;
-	dev_priv = request->i915;
 	ringbuf = request->ringbuf;
 
 	/*
@@ -2895,12 +2913,6 @@ void __i915_add_request(struct drm_i915_gem_request *request,
 	}
 	/* Not allowed to fail! */
 	WARN(ret, "emit|add_request failed: %d!\n", ret);
-
-	queue_delayed_work(dev_priv->wq,
-			   &dev_priv->mm.retire_work,
-			   round_jiffies_up_relative(HZ));
-	intel_mark_busy(dev_priv);
-
 	/* Sanity check that the reserved size was large enough. */
 	ret = intel_ring_get_tail(ringbuf) - request_start;
 	if (ret < 0)
@@ -2909,6 +2921,8 @@ void __i915_add_request(struct drm_i915_gem_request *request,
 		  "Not enough space reserved (%d bytes) "
 		  "for adding the request (%d bytes)\n",
 		  reserved_tail, ret);
+
+	i915_gem_mark_busy(engine);
 }
 
 static bool i915_context_is_banned(struct drm_i915_private *dev_priv,
@@ -3223,72 +3237,105 @@ i915_gem_retire_requests_ring(struct intel_engine_cs *engine)
 	WARN_ON(i915_verify_lists(engine->dev));
 }
 
-bool
-i915_gem_retire_requests(struct drm_i915_private *dev_priv)
+void i915_gem_retire_requests(struct drm_i915_private *dev_priv)
 {
 	struct intel_engine_cs *engine;
-	bool idle = true;
+
+	lockdep_assert_held(&dev_priv->dev->struct_mutex);
+
+	if (dev_priv->gt.active_engines == 0)
+		return;
+
+	GEM_BUG_ON(!dev_priv->gt.awake);
 
 	for_each_engine(engine, dev_priv) {
 		i915_gem_retire_requests_ring(engine);
-		idle &= list_empty(&engine->request_list);
-		if (i915.enable_execlists) {
-			spin_lock_bh(&engine->execlist_lock);
-			idle &= list_empty(&engine->execlist_queue);
-			spin_unlock_bh(&engine->execlist_lock);
-		}
+		if (list_empty(&engine->request_list))
+			dev_priv->gt.active_engines &= ~intel_engine_flag(engine);
 	}
 
-	if (idle)
+	if (dev_priv->gt.active_engines == 0)
 		mod_delayed_work(dev_priv->wq,
-				 &dev_priv->mm.idle_work,
+				 &dev_priv->gt.idle_work,
 				 msecs_to_jiffies(100));
-
-	return idle;
 }
 
 static void
 i915_gem_retire_work_handler(struct work_struct *work)
 {
 	struct drm_i915_private *dev_priv =
-		container_of(work, typeof(*dev_priv), mm.retire_work.work);
+		container_of(work, typeof(*dev_priv), gt.retire_work.work);
 	struct drm_device *dev = dev_priv->dev;
-	bool idle;
 
 	/* Come back later if the device is busy... */
-	idle = false;
 	if (mutex_trylock(&dev->struct_mutex)) {
-		idle = i915_gem_retire_requests(dev_priv);
+		i915_gem_retire_requests(dev_priv);
 		mutex_unlock(&dev->struct_mutex);
 	}
-	if (!idle)
-		queue_delayed_work(dev_priv->wq, &dev_priv->mm.retire_work,
+
+	/* Keep the retire handler running until we are finally idle.
+	 * We do not need to do this test under locking as in the worst-case
+	 * we queue the retire worker once too often.
+	 */
+	if (lockless_dereference(dev_priv->gt.awake))
+		queue_delayed_work(dev_priv->wq,
+				   &dev_priv->gt.retire_work,
 				   round_jiffies_up_relative(HZ));
 }
 
 static void
 i915_gem_idle_work_handler(struct work_struct *work)
 {
 	struct drm_i915_private *dev_priv =
-		container_of(work, typeof(*dev_priv), mm.idle_work.work);
+		container_of(work, typeof(*dev_priv), gt.idle_work.work);
 	struct drm_device *dev = dev_priv->dev;
 	struct intel_engine_cs *engine;
+	unsigned int stuck_engines;
+	bool rearm_hangcheck;
+
+	if (!READ_ONCE(dev_priv->gt.awake))
+		return;
+
+	if (READ_ONCE(dev_priv->gt.active_engines))
+		return;
+
+	rearm_hangcheck =
+		cancel_delayed_work_sync(&dev_priv->gpu_error.hangcheck_work);
+
+	if (!mutex_trylock(&dev->struct_mutex)) {
+		/* Currently busy, come back later */
+		mod_delayed_work(dev_priv->wq,
+				 &dev_priv->gt.idle_work,
+				 msecs_to_jiffies(50));
+		goto out_rearm;
+	}
+
+	if (dev_priv->gt.active_engines)
+		goto out_unlock;
 
 	for_each_engine(engine, dev_priv)
-		if (!list_empty(&engine->request_list))
-			return;
+		i915_gem_batch_pool_fini(&engine->batch_pool);
 
-	/* we probably should sync with hangcheck here, using cancel_work_sync.
-	 * Also locking seems to be fubar here, engine->request_list is protected
-	 * by dev->struct_mutex. */
+	GEM_BUG_ON(!dev_priv->gt.awake);
+	dev_priv->gt.awake = false;
+	rearm_hangcheck = false;
 
-	intel_mark_idle(dev_priv);
+	stuck_engines = intel_kick_waiters(dev_priv);
+	if (unlikely(stuck_engines)) {
+		DRM_DEBUG_DRIVER("kicked stuck waiters...missed irq\n");
+		dev_priv->gpu_error.missed_irq_rings |= stuck_engines;
+	}
 
-	if (mutex_trylock(&dev->struct_mutex)) {
-		for_each_engine(engine, dev_priv)
-			i915_gem_batch_pool_fini(&engine->batch_pool);
+	if (INTEL_GEN(dev_priv) >= 6)
+		gen6_rps_idle(dev_priv);
+	intel_runtime_pm_put(dev_priv);
+out_unlock:
+	mutex_unlock(&dev->struct_mutex);
 
-		mutex_unlock(&dev->struct_mutex);
+out_rearm:
+	if (rearm_hangcheck) {
+		GEM_BUG_ON(!dev_priv->gt.awake);
+		i915_queue_hangcheck(dev_priv);
 	}
 }
 
@@ -4421,7 +4468,7 @@ i915_gem_ring_throttle(struct drm_device *dev, struct drm_file *file)
 
 	ret = __i915_wait_request(target, true, NULL, NULL);
 	if (ret == 0)
-		queue_delayed_work(dev_priv->wq, &dev_priv->mm.retire_work, 0);
+		queue_delayed_work(dev_priv->wq, &dev_priv->gt.retire_work, 0);
 
 	i915_gem_request_unreference(target);
 
@@ -4939,13 +4986,13 @@ i915_gem_suspend(struct drm_device *dev)
 	mutex_unlock(&dev->struct_mutex);
 
 	cancel_delayed_work_sync(&dev_priv->gpu_error.hangcheck_work);
-	cancel_delayed_work_sync(&dev_priv->mm.retire_work);
-	flush_delayed_work(&dev_priv->mm.idle_work);
+	cancel_delayed_work_sync(&dev_priv->gt.retire_work);
+	flush_delayed_work(&dev_priv->gt.idle_work);
 
 	/* Assert that we sucessfully flushed all the work and
 	 * reset the GPU back to its idle, low power state.
 	 */
-	WARN_ON(dev_priv->mm.busy);
+	WARN_ON(dev_priv->gt.awake);
 
 	return 0;
 
@@ -5247,9 +5294,9 @@ i915_gem_load_init(struct drm_device *dev)
 		init_engine_lists(&dev_priv->engine[i]);
 	for (i = 0; i < I915_MAX_NUM_FENCES; i++)
 		INIT_LIST_HEAD(&dev_priv->fence_regs[i].lru_list);
-	INIT_DELAYED_WORK(&dev_priv->mm.retire_work,
+	INIT_DELAYED_WORK(&dev_priv->gt.retire_work,
 			  i915_gem_retire_work_handler);
-	INIT_DELAYED_WORK(&dev_priv->mm.idle_work,
+	INIT_DELAYED_WORK(&dev_priv->gt.idle_work,
 			  i915_gem_idle_work_handler);
 	init_waitqueue_head(&dev_priv->gpu_error.wait_queue);
 	init_waitqueue_head(&dev_priv->gpu_error.reset_queue);

drivers/gpu/drm/i915/i915_gem_execbuffer.c

@@ -1477,6 +1477,12 @@ i915_gem_do_execbuffer(struct drm_device *dev, void *data,
 		dispatch_flags |= I915_DISPATCH_RS;
 	}
 
+	/* Take a local wakeref for preparing to dispatch the execbuf as
+	 * we expect to access the hardware fairly frequently in the
+	 * process. Upon first dispatch, we acquire another prolonged
+	 * wakeref that we hold until the GPU has been idle for at least
+	 * 100ms.
+	 */
 	intel_runtime_pm_get(dev_priv);
 
 	ret = i915_mutex_lock_interruptible(dev);

drivers/gpu/drm/i915/i915_irq.c

@@ -3103,12 +3103,8 @@ static void i915_hangcheck_elapsed(struct work_struct *work)
 	if (!i915.enable_hangcheck)
 		return;
 
-	/*
-	 * The hangcheck work is synced during runtime suspend, we don't
-	 * require a wakeref. TODO: instead of disabling the asserts make
-	 * sure that we hold a reference when this work is running.
-	 */
-	DISABLE_RPM_WAKEREF_ASSERTS(dev_priv);
+	if (!lockless_dereference(dev_priv->gt.awake))
+		return;
 
 	/* As enabling the GPU requires fairly extensive mmio access,
 	 * periodically arm the mmio checker to see if we are triggering
@@ -3216,17 +3212,12 @@ static void i915_hangcheck_elapsed(struct work_struct *work)
 		}
 	}
 
-	if (rings_hung) {
+	if (rings_hung)
 		i915_handle_error(dev_priv, rings_hung, "Engine(s) hung");
-		goto out;
-	}
 
 	/* Reset timer in case GPU hangs without another request being added */
 	if (busy_count)
 		i915_queue_hangcheck(dev_priv);
-
-out:
-	ENABLE_RPM_WAKEREF_ASSERTS(dev_priv);
 }
 
 static void ibx_irq_reset(struct drm_device *dev)