[PATCH] drm: Apply kref_put_mutex() optimisations to drm_gem_object_unreference_unlocked()

[Daniel Vetter]

On Tue, Aug 06, 2013 at 09:59:46AM +0100, Chris Wilson wrote:
> We can apply the same optimisation tricks as kref_put_mutex() in our
> local equivalent function. However, we have a different locking semantic
> (we unlock ourselves, in kref_put_mutex() the callee unlocks) so that we
> can use the same callbacks for both locked and unlocked kref_put()s and
> so can not simply convert to using kref_put_mutex() directly.
> 
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>

I think longterm we want to move to delayed free callbacks (similar to how
fput works) since the locking with dma-buf and all will simply get too
hairy. But for now this is a neat optimization imo, so

Reviewed-by: Daniel Vetter <daniel.vetter at ffwll.ch>
> ---
>  include/drm/drmP.h | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/include/drm/drmP.h b/include/drm/drmP.h
> index 4b518e0..ee2ef27 100644
> --- a/include/drm/drmP.h
> +++ b/include/drm/drmP.h
> @@ -1626,10 +1626,12 @@ drm_gem_object_unreference(struct drm_gem_object *obj)
>  static inline void
>  drm_gem_object_unreference_unlocked(struct drm_gem_object *obj)
>  {
> -	if (obj != NULL) {
> +	if (obj && !atomic_add_unless(&obj->refcount.refcount, -1, 1)) {
>  		struct drm_device *dev = obj->dev;
> +
>  		mutex_lock(&dev->struct_mutex);
> -		kref_put(&obj->refcount, drm_gem_object_free);
> +		if (likely(atomic_dec_and_test(&obj->refcount.refcount)))
> +			drm_gem_object_free(&obj->refcount);
>  		mutex_unlock(&dev->struct_mutex);
>  	}
>  }
> -- 
> 1.8.4.rc1
> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch