drm/i915: Eliminate drm_gem_object_lookup during relocation

As we provide a list of all objects that will be accessed from the
batchbuffer, we can build a lut of the handles associated with those
objects for this invocation and use that to avoid the overhead of
looking up those objects again for every relocation.

The cost of building and searching a small hash table is much less than
that of acquiring a spinlock, searching a radix tree and manipulating an
atomic refcnt per relocation.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

drivers/gpu/drm/i915/i915_drv.h

@@ -788,6 +788,12 @@ struct drm_i915_gem_object {
 	struct scatterlist *sg_list;
 	int num_sg;
 
+	/**
+	 * Used for performing relocations during execbuffer insertion.
+	 */
+	struct hlist_node exec_node;
+	unsigned long exec_handle;
+
 	/**
 	 * Current offset of the object in GTT space.
 	 *

drivers/gpu/drm/i915/i915_gem_execbuffer.c

@@ -207,9 +207,67 @@ i915_gem_object_set_to_gpu_domain(struct drm_i915_gem_object *obj,
 		cd->flush_rings |= ring->id;
 }
 
+struct eb_objects {
+	int and;
+	struct hlist_head buckets[0];
+};
+
+static struct eb_objects *
+eb_create(int size)
+{
+	struct eb_objects *eb;
+	int count = PAGE_SIZE / sizeof(struct hlist_head) / 2;
+	while (count > size)
+		count >>= 1;
+	eb = kzalloc(count*sizeof(struct hlist_head) +
+		     sizeof(struct eb_objects),
+		     GFP_KERNEL);
+	if (eb == NULL)
+		return eb;
+
+	eb->and = count - 1;
+	return eb;
+}
+
+static void
+eb_reset(struct eb_objects *eb)
+{
+	memset(eb->buckets, 0, (eb->and+1)*sizeof(struct hlist_head));
+}
+
+static void
+eb_add_object(struct eb_objects *eb, struct drm_i915_gem_object *obj)
+{
+	hlist_add_head(&obj->exec_node,
+		       &eb->buckets[obj->exec_handle & eb->and]);
+}
+
+static struct drm_i915_gem_object *
+eb_get_object(struct eb_objects *eb, unsigned long handle)
+{
+	struct hlist_head *head;
+	struct hlist_node *node;
+	struct drm_i915_gem_object *obj;
+
+	head = &eb->buckets[handle & eb->and];
+	hlist_for_each(node, head) {
+		obj = hlist_entry(node, struct drm_i915_gem_object, exec_node);
+		if (obj->exec_handle == handle)
+			return obj;
+	}
+
+	return NULL;
+}
+
+static void
+eb_destroy(struct eb_objects *eb)
+{
+	kfree(eb);
+}
+
 static int
 i915_gem_execbuffer_relocate_entry(struct drm_i915_gem_object *obj,
-				   struct drm_file *file_priv,
+				   struct eb_objects *eb,
 				   struct drm_i915_gem_exec_object2 *entry,
 				   struct drm_i915_gem_relocation_entry *reloc)
 {
@@ -218,9 +276,9 @@ i915_gem_execbuffer_relocate_entry(struct drm_i915_gem_object *obj,
 	uint32_t target_offset;
 	int ret = -EINVAL;
 
-	target_obj = drm_gem_object_lookup(dev, file_priv,
-					   reloc->target_handle);
-	if (target_obj == NULL)
+	/* we've already hold a reference to all valid objects */
+	target_obj = &eb_get_object(eb, reloc->target_handle)->base;
+	if (unlikely(target_obj == NULL))
 		return -ENOENT;
 
 	target_offset = to_intel_bo(target_obj)->gtt_offset;
@@ -246,7 +304,7 @@ i915_gem_execbuffer_relocate_entry(struct drm_i915_gem_object *obj,
 	if (target_offset == 0) {
 		DRM_ERROR("No GTT space found for object %d\n",
 			  reloc->target_handle);
-		goto err;
+		return ret;
 	}
 
 	/* Validate that the target is in a valid r/w GPU domain */
@@ -258,7 +316,7 @@ i915_gem_execbuffer_relocate_entry(struct drm_i915_gem_object *obj,
 			  (int) reloc->offset,
 			  reloc->read_domains,
 			  reloc->write_domain);
-		goto err;
+		return ret;
 	}
 	if (reloc->write_domain & I915_GEM_DOMAIN_CPU ||
 	    reloc->read_domains & I915_GEM_DOMAIN_CPU) {
@@ -269,7 +327,7 @@ i915_gem_execbuffer_relocate_entry(struct drm_i915_gem_object *obj,
 			  (int) reloc->offset,
 			  reloc->read_domains,
 			  reloc->write_domain);
-		goto err;
+		return ret;
 	}
 	if (reloc->write_domain && target_obj->pending_write_domain &&
 	    reloc->write_domain != target_obj->pending_write_domain) {
@@ -280,7 +338,7 @@ i915_gem_execbuffer_relocate_entry(struct drm_i915_gem_object *obj,
 			  (int) reloc->offset,
 			  reloc->write_domain,
 			  target_obj->pending_write_domain);
-		goto err;
+		return ret;
 	}
 
 	target_obj->pending_read_domains |= reloc->read_domains;
@@ -290,7 +348,7 @@ i915_gem_execbuffer_relocate_entry(struct drm_i915_gem_object *obj,
 	 * more work needs to be done.
 	 */
 	if (target_offset == reloc->presumed_offset)
-		goto out;
+		return 0;
 
 	/* Check that the relocation address is valid... */
 	if (reloc->offset > obj->base.size - 4) {
@@ -299,14 +357,14 @@ i915_gem_execbuffer_relocate_entry(struct drm_i915_gem_object *obj,
 			  obj, reloc->target_handle,
 			  (int) reloc->offset,
 			  (int) obj->base.size);
-		goto err;
+		return ret;
 	}
 	if (reloc->offset & 3) {
 		DRM_ERROR("Relocation not 4-byte aligned: "
 			  "obj %p target %d offset %d.\n",
 			  obj, reloc->target_handle,
 			  (int) reloc->offset);
-		goto err;
+		return ret;
 	}
 
 	/* and points to somewhere within the target object. */
@@ -316,7 +374,7 @@ i915_gem_execbuffer_relocate_entry(struct drm_i915_gem_object *obj,
 			  obj, reloc->target_handle,
 			  (int) reloc->delta,
 			  (int) target_obj->size);
-		goto err;
+		return ret;
 	}
 
 	reloc->delta += target_offset;
@@ -334,7 +392,7 @@ i915_gem_execbuffer_relocate_entry(struct drm_i915_gem_object *obj,
 
 		ret = i915_gem_object_set_to_gtt_domain(obj, 1);
 		if (ret)
-			goto err;
+			return ret;
 
 		/* Map the page containing the relocation we're going to perform.  */
 		reloc->offset += obj->gtt_offset;
@@ -349,16 +407,12 @@ i915_gem_execbuffer_relocate_entry(struct drm_i915_gem_object *obj,
 	/* and update the user's relocation entry */
 	reloc->presumed_offset = target_offset;
 
-out:
-	ret = 0;
-err:
-	drm_gem_object_unreference(target_obj);
-	return ret;
+	return 0;
 }
 
 static int
 i915_gem_execbuffer_relocate_object(struct drm_i915_gem_object *obj,
-				    struct drm_file *file_priv,
+				    struct eb_objects *eb,
 				    struct drm_i915_gem_exec_object2 *entry)
 {
 	struct drm_i915_gem_relocation_entry __user *user_relocs;
@@ -373,7 +427,7 @@ i915_gem_execbuffer_relocate_object(struct drm_i915_gem_object *obj,
 					      sizeof(reloc)))
 			return -EFAULT;
 
-		ret = i915_gem_execbuffer_relocate_entry(obj, file_priv, entry, &reloc);
+		ret = i915_gem_execbuffer_relocate_entry(obj, eb, entry, &reloc);
 		if (ret)
 			return ret;
 
@@ -388,14 +442,14 @@ i915_gem_execbuffer_relocate_object(struct drm_i915_gem_object *obj,
 
 static int
 i915_gem_execbuffer_relocate_object_slow(struct drm_i915_gem_object *obj,
-					 struct drm_file *file_priv,
+					 struct eb_objects *eb,
 					 struct drm_i915_gem_exec_object2 *entry,
 					 struct drm_i915_gem_relocation_entry *relocs)
 {
 	int i, ret;
 
 	for (i = 0; i < entry->relocation_count; i++) {
-		ret = i915_gem_execbuffer_relocate_entry(obj, file_priv, entry, &relocs[i]);
+		ret = i915_gem_execbuffer_relocate_entry(obj, eb, entry, &relocs[i]);
 		if (ret)
 			return ret;
 	}
@@ -405,7 +459,7 @@ i915_gem_execbuffer_relocate_object_slow(struct drm_i915_gem_object *obj,
 
 static int
 i915_gem_execbuffer_relocate(struct drm_device *dev,
-			     struct drm_file *file,
+			     struct eb_objects *eb,
 			     struct list_head *objects,
 			     struct drm_i915_gem_exec_object2 *exec)
 {
@@ -415,7 +469,7 @@ i915_gem_execbuffer_relocate(struct drm_device *dev,
 	list_for_each_entry(obj, objects, exec_list) {
 		obj->base.pending_read_domains = 0;
 		obj->base.pending_write_domain = 0;
-		ret = i915_gem_execbuffer_relocate_object(obj, file, exec++);
+		ret = i915_gem_execbuffer_relocate_object(obj, eb, exec++);
 		if (ret)
 			return ret;
 	}
@@ -560,6 +614,7 @@ i915_gem_execbuffer_relocate_slow(struct drm_device *dev,
 				  struct drm_file *file,
 				  struct intel_ring_buffer *ring,
 				  struct list_head *objects,
+				  struct eb_objects *eb,
 				  struct drm_i915_gem_exec_object2 *exec,
 				  int count)
 {
@@ -567,6 +622,15 @@ i915_gem_execbuffer_relocate_slow(struct drm_device *dev,
 	struct drm_i915_gem_object *obj;
 	int i, total, ret;
 
+	/* We may process another execbuffer during the unlock... */
+	while (list_empty(objects)) {
+		obj = list_first_entry(objects,
+				       struct drm_i915_gem_object,
+				       exec_list);
+		list_del_init(&obj->exec_list);
+		drm_gem_object_unreference(&obj->base);
+	}
+
 	mutex_unlock(&dev->struct_mutex);
 
 	total = 0;
@@ -601,6 +665,26 @@ i915_gem_execbuffer_relocate_slow(struct drm_device *dev,
 		goto err;
 	}
 
+	/* reacquire the objects */
+	INIT_LIST_HEAD(objects);
+	eb_reset(eb);
+	for (i = 0; i < count; i++) {
+		struct drm_i915_gem_object *obj;
+
+		obj = to_intel_bo(drm_gem_object_lookup(dev, file,
+							exec[i].handle));
+		if (obj == NULL) {
+			DRM_ERROR("Invalid object handle %d at index %d\n",
+				   exec[i].handle, i);
+			ret = -ENOENT;
+			goto err;
+		}
+
+		list_add_tail(&obj->exec_list, objects);
+		obj->exec_handle = exec[i].handle;
+		eb_add_object(eb, obj);
+	}
+
 	ret = i915_gem_execbuffer_reserve(ring, file, objects, exec);
 	if (ret)
 		goto err;
@@ -609,7 +693,7 @@ i915_gem_execbuffer_relocate_slow(struct drm_device *dev,
 	list_for_each_entry(obj, objects, exec_list) {
 		obj->base.pending_read_domains = 0;
 		obj->base.pending_write_domain = 0;
-		ret = i915_gem_execbuffer_relocate_object_slow(obj, file,
+		ret = i915_gem_execbuffer_relocate_object_slow(obj, eb,
 							       exec,
 							       reloc + total);
 		if (ret)
@@ -868,6 +952,7 @@ i915_gem_do_execbuffer(struct drm_device *dev, void *data,
 {
 	drm_i915_private_t *dev_priv = dev->dev_private;
 	struct list_head objects;
+	struct eb_objects *eb;
 	struct drm_i915_gem_object *batch_obj;
 	struct drm_clip_rect *cliprects = NULL;
 	struct intel_ring_buffer *ring;
@@ -950,6 +1035,13 @@ i915_gem_do_execbuffer(struct drm_device *dev, void *data,
 		goto pre_mutex_err;
 	}
 
+	eb = eb_create(args->buffer_count);
+	if (eb == NULL) {
+		mutex_unlock(&dev->struct_mutex);
+		ret = -ENOMEM;
+		goto pre_mutex_err;
+	}
+
 	/* Look up object handles */
 	INIT_LIST_HEAD(&objects);
 	for (i = 0; i < args->buffer_count; i++) {
@@ -973,6 +1065,8 @@ i915_gem_do_execbuffer(struct drm_device *dev, void *data,
 		}
 
 		list_add_tail(&obj->exec_list, &objects);
+		obj->exec_handle = exec[i].handle;
+		eb_add_object(eb, obj);
 	}
 
 	/* Move the objects en-masse into the GTT, evicting if necessary. */
@@ -981,11 +1075,12 @@ i915_gem_do_execbuffer(struct drm_device *dev, void *data,
 		goto err;
 
 	/* The objects are in their final locations, apply the relocations. */
-	ret = i915_gem_execbuffer_relocate(dev, file, &objects, exec);
+	ret = i915_gem_execbuffer_relocate(dev, eb, &objects, exec);
 	if (ret) {
 		if (ret == -EFAULT) {
 			ret = i915_gem_execbuffer_relocate_slow(dev, file, ring,
-								&objects, exec,
+								&objects, eb,
+								exec,
 								args->buffer_count);
 			BUG_ON(!mutex_is_locked(&dev->struct_mutex));
 		}
@@ -1051,6 +1146,7 @@ i915_gem_do_execbuffer(struct drm_device *dev, void *data,
 	i915_gem_execbuffer_retire_commands(dev, file, ring);
 
 err:
+	eb_destroy(eb);
 	while (!list_empty(&objects)) {
 		struct drm_i915_gem_object *obj;