drm/i915: Only track live rings for retiring

We don't need to track every ring for its lifetime as they are managed
by the contexts/engines. What we do want to track are the live rings so
that we can sporadically clean up requests if userspace falls behind. We
can simply restrict the gt->rings list to being only gt->live_rings.

v2: s/live/active/ for consistency with gt.active_requests
Suggested-by: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180430131503.5375-4-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_drv.h

@@ -2061,7 +2061,8 @@ struct drm_i915_private {
 
 		struct i915_gem_timeline global_timeline;
 		struct list_head timelines;
-		struct list_head rings;
+
+		struct list_head active_rings;
 		u32 active_requests;
 		u32 request_serial;
 

drivers/gpu/drm/i915/i915_gem.c

@@ -141,6 +141,7 @@ static u32 __i915_gem_park(struct drm_i915_private *i915)
 {
 	lockdep_assert_held(&i915->drm.struct_mutex);
 	GEM_BUG_ON(i915->gt.active_requests);
+	GEM_BUG_ON(!list_empty(&i915->gt.active_rings));
 
 	if (!i915->gt.awake)
 		return I915_EPOCH_INVALID;
@@ -5599,9 +5600,10 @@ int i915_gem_init_early(struct drm_i915_private *dev_priv)
 	if (!dev_priv->priorities)
 		goto err_dependencies;
 
-	mutex_lock(&dev_priv->drm.struct_mutex);
-	INIT_LIST_HEAD(&dev_priv->gt.rings);
 	INIT_LIST_HEAD(&dev_priv->gt.timelines);
+	INIT_LIST_HEAD(&dev_priv->gt.active_rings);
+
+	mutex_lock(&dev_priv->drm.struct_mutex);
 	err = i915_gem_timeline_init__global(dev_priv);
 	mutex_unlock(&dev_priv->drm.struct_mutex);
 	if (err)

drivers/gpu/drm/i915/i915_request.c

@@ -322,6 +322,7 @@ static void advance_ring(struct i915_request *request)
 		 * noops - they are safe to be replayed on a reset.
 		 */
 		tail = READ_ONCE(request->tail);
+		list_del(&ring->active_link);
 	} else {
 		tail = request->postfix;
 	}
@@ -1096,6 +1097,8 @@ void __i915_request_add(struct i915_request *request, bool flush_caches)
 	i915_gem_active_set(&timeline->last_request, request);
 
 	list_add_tail(&request->ring_link, &ring->request_list);
+	if (list_is_first(&request->ring_link, &ring->request_list))
+		list_add(&ring->active_link, &request->i915->gt.active_rings);
 	request->emitted_jiffies = jiffies;
 
 	/*
@@ -1418,14 +1421,17 @@ static void ring_retire_requests(struct intel_ring *ring)
 
 void i915_retire_requests(struct drm_i915_private *i915)
 {
-	struct intel_ring *ring, *next;
+	struct intel_ring *ring, *tmp;
 
 	lockdep_assert_held(&i915->drm.struct_mutex);
 
 	if (!i915->gt.active_requests)
 		return;
 
-	list_for_each_entry_safe(ring, next, &i915->gt.rings, link)
+	/* An outstanding request must be on a still active ring somewhere */
+	GEM_BUG_ON(list_empty(&i915->gt.active_rings));
+
+	list_for_each_entry_safe(ring, tmp, &i915->gt.active_rings, active_link)
 		ring_retire_requests(ring);
 }
 

drivers/gpu/drm/i915/intel_ringbuffer.c

@@ -1150,8 +1150,6 @@ intel_engine_create_ring(struct intel_engine_cs *engine, int size)
 	}
 	ring->vma = vma;
 
-	list_add(&ring->link, &engine->i915->gt.rings);
-
 	return ring;
 }
 
@@ -1163,8 +1161,6 @@ intel_ring_free(struct intel_ring *ring)
 	i915_vma_close(ring->vma);
 	__i915_gem_object_release_unless_active(obj);
 
-	list_del(&ring->link);
-
 	kfree(ring);
 }
 

drivers/gpu/drm/i915/intel_ringbuffer.h

@@ -130,7 +130,7 @@ struct intel_ring {
 	void *vaddr;
 
 	struct list_head request_list;
-	struct list_head link;
+	struct list_head active_link;
 
 	u32 head;
 	u32 tail;

drivers/gpu/drm/i915/selftests/mock_engine.c

@@ -147,15 +147,11 @@ static struct intel_ring *mock_ring(struct intel_engine_cs *engine)
 	INIT_LIST_HEAD(&ring->request_list);
 	intel_ring_update_space(ring);
 
-	list_add(&ring->link, &engine->i915->gt.rings);
-
 	return ring;
 }
 
 static void mock_ring_free(struct intel_ring *ring)
 {
-	list_del(&ring->link);
-
 	kfree(ring);
 }
 

drivers/gpu/drm/i915/selftests/mock_gem_device.c

@@ -224,9 +224,10 @@ struct drm_i915_private *mock_gem_device(void)
 	if (!i915->priorities)
 		goto err_dependencies;
 
-	mutex_lock(&i915->drm.struct_mutex);
-	INIT_LIST_HEAD(&i915->gt.rings);
 	INIT_LIST_HEAD(&i915->gt.timelines);
+	INIT_LIST_HEAD(&i915->gt.active_rings);
+
+	mutex_lock(&i915->drm.struct_mutex);
 	err = i915_gem_timeline_init__global(i915);
 	if (err) {
 		mutex_unlock(&i915->drm.struct_mutex);