[PATCH] locking/qspinlock: Use atomic_sub_return_release in queued_spin_unlock

From	Pan Xinhui <xinhui.pan@linux.vnet.ibm.com>
Newsgroups	linux.kernel
Subject	[PATCH] locking/qspinlock: Use atomic_sub_return_release in queued_spin_unlock
Date	2016-06-03 10:40 +0200
Message-ID	<rFSO5-PO-3@gated-at.bofh.it> (permalink)
Organization	linux.* mail to news gateway

Show all headers | View raw

The existing version uses a heavy barrier while only release semantics
is required. So use atomic_sub_return_release instead.

Suggested-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Pan Xinhui <xinhui.pan@linux.vnet.ibm.com>
---
 include/asm-generic/qspinlock.h | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/include/asm-generic/qspinlock.h b/include/asm-generic/qspinlock.h
index 35a52a8..8947cd2 100644
--- a/include/asm-generic/qspinlock.h
+++ b/include/asm-generic/qspinlock.h
@@ -92,10 +92,9 @@ static __always_inline void queued_spin_lock(struct qspinlock *lock)
 static __always_inline void queued_spin_unlock(struct qspinlock *lock)
 {
 	/*
-	 * smp_mb__before_atomic() in order to guarantee release semantics
-	 */
-	smp_mb__before_atomic();
-	atomic_sub(_Q_LOCKED_VAL, &lock->val);
+	* unlock() need release semantics
+	*/
+	(void)atomic_sub_return_release(_Q_LOCKED_VAL, &lock->val);
 }
 #endif
 
-- 
1.9.1

Back to linux.kernel | Previous | Next — Next in thread | Find similar | Unroll thread

Thread

[PATCH] locking/qspinlock: Use atomic_sub_return_release in queued_spin_unlock Pan Xinhui <xinhui.pan@linux.vnet.ibm.com> - 2016-06-03 10:40 +0200
  [tip:locking/core] locking/qspinlock: Use  atomic_sub_return_release() in queued_spin_unlock() tip-bot for Pan Xinhui <tipbot@zytor.com> - 2016-06-08 16:30 +0200

csiph-web