linux-kernel - [PATCH] drm/i915/active: Use try_cmpxchg() in active_fence

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Message-ID: <20241003084533.871524-1-ubizjak@gmail.com>
Date: Thu,  3 Oct 2024 10:44:31 +0200
From: Uros Bizjak <ubizjak@...il.com>
To: intel-gfx@...ts.freedesktop.org,
	dri-devel@...ts.freedesktop.org,
	linux-kernel@...r.kernel.org
Cc: Uros Bizjak <ubizjak@...il.com>,
	Jani Nikula <jani.nikula@...ux.intel.com>,
	Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
	Rodrigo Vivi <rodrigo.vivi@...el.com>,
	Tvrtko Ursulin <tursulin@...ulin.net>,
	David Airlie <airlied@...il.com>,
	Simona Vetter <simona@...ll.ch>
Subject: [PATCH] drm/i915/active: Use try_cmpxchg() in active_fence_cb()

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@...il.com>
Cc: Jani Nikula <jani.nikula@...ux.intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@...el.com>
Cc: Tvrtko Ursulin <tursulin@...ulin.net>
Cc: David Airlie <airlied@...il.com>
Cc: Simona Vetter <simona@...ll.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