linux-kernel - [PATCH] arch/tile: use atomic exchange in arch_write

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Message-Id: <201203302105.q2UL58Z8006306@farm-0012.internal.tilera.com>
Date:	Fri, 30 Mar 2012 15:46:29 -0400
From:	Chris Metcalf <cmetcalf@...era.com>
To:	Chris Metcalf <cmetcalf@...era.com>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	linux-kernel@...r.kernel.org
Subject: [PATCH] arch/tile: use atomic exchange in arch_write_unlock()

This idiom is used elsewhere when we do an unlock by writing a zero,
but I missed it here.  Using an atomic operation avoids waiting
on the write buffer for the unlocking write to be sent to the home cache.

Signed-off-by: Chris Metcalf <cmetcalf@...era.com>
---
 arch/tile/include/asm/spinlock_64.h |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/arch/tile/include/asm/spinlock_64.h b/arch/tile/include/asm/spinlock_64.h
index 72be590..5f8b6a0 100644
--- a/arch/tile/include/asm/spinlock_64.h
+++ b/arch/tile/include/asm/spinlock_64.h
@@ -137,7 +137,7 @@ static inline void arch_read_unlock(arch_rwlock_t *rw)
 static inline void arch_write_unlock(arch_rwlock_t *rw)
 {
 	__insn_mf();
-	rw->lock = 0;
+	__insn_exch4(&rw->lock, 0);  /* Avoid waiting in the write buffer. */
 }
 
 static inline int arch_read_trylock(arch_rwlock_t *rw)
-- 
1.6.5.2

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