[PATCH 2/3] drm: Only bump object-reference count when adding first handle

Chris Wilson
2016-01-04T10:11:00Z

We only need a single reference count for all handles (i.e. non-zero
obj->handle_count) and so can trim a few atomic operations by only
taking the reference on the first handle and dropping it after the last.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
---
drivers/gpu/drm/drm_gem.c | 17 ++++++++++++-----
1 file changed, 12 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c
index a08176debc0e..ad955d7c99fd 100644
--- a/drivers/gpu/drm/drm_gem.c
+++ b/drivers/gpu/drm/drm_gem.c
@@ -220,6 +220,9 @@ static void drm_gem_object_exported_dma_buf_free(struct drm_gem_object *obj)
static void
drm_gem_object_handle_unreference_unlocked(struct drm_gem_object *obj)
{
+ struct drm_device *dev = obj->dev;
+ bool final = false;
+
if (WARN_ON(obj->handle_count == 0))
return;

@@ -229,14 +232,16 @@ drm_gem_object_handle_unreference_unlocked(struct drm_gem_object *obj)
* checked for a name
*/

- mutex_lock(&obj->dev->object_name_lock);
+ mutex_lock(&dev->object_name_lock);
if (--obj->handle_count == 0) {
drm_gem_object_handle_free(obj);
drm_gem_object_exported_dma_buf_free(obj);
+ final = true;
}
- mutex_unlock(&obj->dev->object_name_lock);
+ mutex_unlock(&dev->object_name_lock);

- drm_gem_object_unreference_unlocked(obj);
+ if (final)
+ drm_gem_object_unreference_unlocked(obj);
}

/**
@@ -329,6 +334,8 @@ drm_gem_handle_create_tail(struct drm_file *file_priv,
int ret;

WARN_ON(!mutex_is_locked(&dev->object_name_lock));
+ if (obj->handle_count++ == 0)
+ drm_gem_object_reference(obj);

/*
* Get the user-visible handle using idr. Preload and perform
@@ -338,10 +345,10 @@ drm_gem_handle_create_tail(struct drm_file *file_priv,
spin_lock(&file_priv->table_lock);

ret = idr_alloc(&file_priv->object_idr, obj, 1, 0, GFP_NOWAIT);
- drm_gem_object_reference(obj);
- obj->handle_count++;
+
spin_unlock(&file_priv->table_lock);
idr_preload_end();
+
mutex_unlock(&dev->object_name_lock);
if (ret < 0)
goto err_unref;
--
2.6.4