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Fri, 25 Jul 2025 00:27:35 -0700 (PDT) Received: from fedora ([193.77.86.199]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3b76fc7885esm4227301f8f.35.2025.07.25.00.27.34 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 25 Jul 2025 00:27:34 -0700 (PDT) From: Uros Bizjak To: intel-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org Cc: Uros Bizjak , Jani Nikula , Joonas Lahtinen , Rodrigo Vivi , Tvrtko Ursulin , David Airlie , Simona Vetter Subject: [PATCH] drm/i915/active: Use try_cmpxchg64() in __active_lookup() Date: Fri, 25 Jul 2025 09:26:42 +0200 Message-ID: <20250725072727.68486-1-ubizjak@gmail.com> X-Mailer: git-send-email 2.50.1 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Replace this pattern in __active_lookup(): cmpxchg64(*ptr, old, new) =3D=3D old ... with the simpler and faster: try_cmpxchg64(*ptr, &old, new) The x86 CMPXCHG instruction returns success in the ZF flag, so this change saves a compare after the CMPXCHG. The patch also improves the explanation of what the code really does. cmpxchg64() will *succeed* for the winner of the race and try_cmpxchg64() nicely documents this fact. No functional change intended. Signed-off-by: Uros Bizjak Cc: Jani Nikula Cc: Joonas Lahtinen Cc: Rodrigo Vivi Cc: Tvrtko Ursulin Cc: David Airlie Cc: Simona Vetter --- drivers/gpu/drm/i915/i915_active.c | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-) diff --git a/drivers/gpu/drm/i915/i915_active.c b/drivers/gpu/drm/i915/i915= _active.c index 0dbc4e289300..6b0c1162505a 100644 --- a/drivers/gpu/drm/i915/i915_active.c +++ b/drivers/gpu/drm/i915/i915_active.c @@ -257,10 +257,9 @@ static struct active_node *__active_lookup(struct i915= _active *ref, u64 idx) * claimed the cache and we know that is does not match our * idx. If, and only if, the timeline is currently zero is it * worth competing to claim it atomically for ourselves (for - * only the winner of that race will cmpxchg return the old - * value of 0). + * only the winner of that race will cmpxchg succeed). */ - if (!cached && !cmpxchg64(&it->timeline, 0, idx)) + if (!cached && try_cmpxchg64(&it->timeline, &cached, idx)) return it; } =20 --=20 2.50.1