[PATCH 1/2] x86: optimize a bit __raw_read_trylock
From: Frederic Weisbecker
Date: Sun Jan 25 2009 - 15:50:29 EST
The current version of __raw_read_trylock starts with decrementing the lock
and read its new value as a separate operation after that.
That makes 3 dereferences (read, write (after sub), read) whereas
a single atomic_dec_return does only two pointers dereferences (read, write).
Signed-off-by: Frederic Weisbecker <fweisbec@xxxxxxxxx>
---
arch/x86/include/asm/spinlock.h | 3 +--
1 files changed, 1 insertions(+), 2 deletions(-)
diff --git a/arch/x86/include/asm/spinlock.h b/arch/x86/include/asm/spinlock.h
index 2bd6b11..139b424 100644
--- a/arch/x86/include/asm/spinlock.h
+++ b/arch/x86/include/asm/spinlock.h
@@ -267,8 +267,7 @@ static inline int __raw_read_trylock(raw_rwlock_t *lock)
{
atomic_t *count = (atomic_t *)lock;
- atomic_dec(count);
- if (atomic_read(count) >= 0)
+ if (atomic_dec_return(count) >= 0)
return 1;
atomic_inc(count);
return 0;
--
1.6.1
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