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x86: micro-optimize __raw_read_trylock()

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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@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Frederic Weisbecker 2009-01-25 12:50:13 -08:00 committed by Ingo Molnar
parent 7106a5ab89
commit 2d4d57db69
1 changed files with 1 additions and 2 deletions
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3
arch/x86/include/asm/spinlock.h
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@ -329,8 +329,7 @@ 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;