linux-kernel - [PATCH v3 5/6] pv-qspinlock: use cmpxchg_release in __pv_queued_spin

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Date:	Wed, 25 May 2016 16:18:08 +0800
From:	Pan Xinhui <xinhui.pan@...ux.vnet.ibm.com>
To:	linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
	virtualization@...ts.linux-foundation.org
Cc:	benh@...nel.crashing.org, paulus@...ba.org, mpe@...erman.id.au,
	peterz@...radead.org, mingo@...hat.com, paulmck@...ux.vnet.ibm.com,
	jeremy@...p.org, chrisw@...s-sol.org, akataria@...are.com,
	rusty@...tcorp.com.au, Pan Xinhui <xinhui.pan@...ux.vnet.ibm.com>
Subject: [PATCH v3 5/6] pv-qspinlock: use cmpxchg_release in __pv_queued_spin_unlock

cmpxchg_release is light-wight than cmpxchg, we can gain a better
performace then. On some arch like ppc, barrier impact the performace
too much.

Suggested-by:  Boqun Feng <boqun.feng@...il.com>
Signed-off-by: Pan Xinhui <xinhui.pan@...ux.vnet.ibm.com>
---
 kernel/locking/qspinlock_paravirt.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/locking/qspinlock_paravirt.h b/kernel/locking/qspinlock_paravirt.h
index a5b1248..2bbffe4 100644
--- a/kernel/locking/qspinlock_paravirt.h
+++ b/kernel/locking/qspinlock_paravirt.h
@@ -614,7 +614,7 @@ __visible void __pv_queued_spin_unlock(struct qspinlock *lock)
 	 * unhash. Otherwise it would be possible to have multiple @lock
 	 * entries, which would be BAD.
 	 */
-	locked = cmpxchg(&l->locked, _Q_LOCKED_VAL, 0);
+	locked = cmpxchg_release(&l->locked, _Q_LOCKED_VAL, 0);
 	if (likely(locked == _Q_LOCKED_VAL))
 		return;
 
-- 
1.9.1