Replace this pattern in active_fence_cb():

    cmpxchg(*ptr, old, new) == old

... with the simpler and faster:

    try_cmpxchg(*ptr, &old, new)

The x86 CMPXCHG instruction returns success in the ZF flag,
so this change saves a compare after the CMPXCHG.

Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Tvrtko Ursulin <tursulin@ursulin.net>
Cc: David Airlie <airlied@gmail.com>
Cc: Simona Vetter <simona@ffwll.ch>
---
 drivers/gpu/drm/i915/i915_active.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/i915_active.c b/drivers/gpu/drm/i915/i915_active.c
index 5ec293011d99..35319228bc51 100644
--- a/drivers/gpu/drm/i915/i915_active.c
+++ b/drivers/gpu/drm/i915/i915_active.c
@@ -212,7 +212,7 @@ active_fence_cb(struct dma_fence *fence, struct dma_fence_cb *cb)
 	struct i915_active_fence *active =
 		container_of(cb, typeof(*active), cb);
 
-	return cmpxchg(__active_fence_slot(active), fence, NULL) == fence;
+	return try_cmpxchg(__active_fence_slot(active), &fence, NULL);
 }
 
 static void
-- 
2.46.2

On Thu, 03 Oct 2024, Uros Bizjak <ubizjak@gmail.com> wrote:
> Replace this pattern in active_fence_cb():
>
>     cmpxchg(*ptr, old, new) == old
>
> ... with the simpler and faster:
>
>     try_cmpxchg(*ptr, &old, new)
>
> The x86 CMPXCHG instruction returns success in the ZF flag,
> so this change saves a compare after the CMPXCHG.
>
> Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
> Cc: Jani Nikula <jani.nikula@linux.intel.com>
> Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
> Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
> Cc: Tvrtko Ursulin <tursulin@ursulin.net>
> Cc: David Airlie <airlied@gmail.com>
> Cc: Simona Vetter <simona@ffwll.ch>

Pushed to drm-intel-next, thanks for the patch.

BR,
Jani.

> ---
>  drivers/gpu/drm/i915/i915_active.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_active.c b/drivers/gpu/drm/i915/i915_active.c
> index 5ec293011d99..35319228bc51 100644
> --- a/drivers/gpu/drm/i915/i915_active.c
> +++ b/drivers/gpu/drm/i915/i915_active.c
> @@ -212,7 +212,7 @@ active_fence_cb(struct dma_fence *fence, struct dma_fence_cb *cb)
>  	struct i915_active_fence *active =
>  		container_of(cb, typeof(*active), cb);
>  
> -	return cmpxchg(__active_fence_slot(active), fence, NULL) == fence;
> +	return try_cmpxchg(__active_fence_slot(active), &fence, NULL);
>  }
>  
>  static void

-- 
Jani Nikula, Intel