drm/i915: Periodically flush the active lists and requests

In order to retire active buffers whilst no client is active, we need to
insert our own flush requests onto the ring.

This is useful for servers that queue up some rendering and then go to
sleep as it allows us to the complete processing of those requests,
potentially making that memory available again much earlier.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

drivers/gpu/drm/i915/i915_gem.c

@@ -1935,6 +1935,8 @@ i915_gem_retire_work_handler(struct work_struct *work)
 {
 	drm_i915_private_t *dev_priv;
 	struct drm_device *dev;
+	bool idle;
+	int i;
 
 	dev_priv = container_of(work, drm_i915_private_t,
 				mm.retire_work.work);
@@ -1948,11 +1950,31 @@ i915_gem_retire_work_handler(struct work_struct *work)
 
 	i915_gem_retire_requests(dev);
 
-	if (!dev_priv->mm.suspended &&
-		(!list_empty(&dev_priv->ring[RCS].request_list) ||
-		 !list_empty(&dev_priv->ring[VCS].request_list) ||
-		 !list_empty(&dev_priv->ring[BCS].request_list)))
+	/* Send a periodic flush down the ring so we don't hold onto GEM
+	 * objects indefinitely.
+	 */
+	idle = true;
+	for (i = 0; i < I915_NUM_RINGS; i++) {
+		struct intel_ring_buffer *ring = &dev_priv->ring[i];
+
+		if (!list_empty(&ring->gpu_write_list)) {
+			struct drm_i915_gem_request *request;
+			int ret;
+
+			ret = i915_gem_flush_ring(dev, ring, 0,
+						  I915_GEM_GPU_DOMAINS);
+			request = kzalloc(sizeof(*request), GFP_KERNEL);
+			if (ret || request == NULL ||
+			    i915_add_request(dev, NULL, request, ring))
+			    kfree(request);
+		}
+
+		idle &= list_empty(&ring->request_list);
+	}
+
+	if (!dev_priv->mm.suspended && !idle)
 		queue_delayed_work(dev_priv->wq, &dev_priv->mm.retire_work, HZ);
+
 	mutex_unlock(&dev->struct_mutex);
 }