linux-kernel - [PATCH 2/2] locking/rtmutex: optimize rt_mutex

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Message-Id: <1587135032-188866-2-git-send-email-alex.shi@linux.alibaba.com>
Date:   Fri, 17 Apr 2020 22:50:32 +0800
From:   Alex Shi <alex.shi@...ux.alibaba.com>
To:     unlisted-recipients:; (no To-header on input)
Cc:     Alex Shi <alex.shi@...ux.alibaba.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Davidlohr Bueso <dave@...olabs.net>,
        Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>,
        linux-kernel@...r.kernel.org
Subject: [PATCH 2/2] locking/rtmutex: optimize rt_mutex_cmpxchgs

Checking l->owner first to skip time cost cmpxchgs.

Suggested-by: Davidlohr Bueso <dave@...olabs.net>
Signed-off-by: Alex Shi <alex.shi@...ux.alibaba.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Davidlohr Bueso <dave@...olabs.net>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Will Deacon <will@...nel.org>
Cc: linux-kernel@...r.kernel.org
---
 kernel/locking/rtmutex.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
index cfdd5b93264d..232727a4a220 100644
--- a/kernel/locking/rtmutex.c
+++ b/kernel/locking/rtmutex.c
@@ -141,8 +141,10 @@ static void fixup_rt_mutex_waiters(struct rt_mutex *lock)
  * set up.
  */
 #ifndef CONFIG_DEBUG_RT_MUTEXES
-# define rt_mutex_cmpxchg_acquire(l,c,n) (cmpxchg_acquire(&l->owner, c, n) == c)
-# define rt_mutex_cmpxchg_release(l,c,n) (cmpxchg_release(&l->owner, c, n) == c)
+# define rt_mutex_cmpxchg_acquire(l, c, n)	\
+			(l->owner == c && cmpxchg_acquire(&l->owner, c, n) == c)
+# define rt_mutex_cmpxchg_release(l, c, n)	\
+			(l->owner == c && cmpxchg_release(&l->owner, c, n) == c)
 
 /*
  * Callers must hold the ->wait_lock -- which is the whole purpose as we force
-- 
1.8.3.1