Commit 2d4d57db authored Jan 25, 2009 by Frederic Weisbecker Committed by Ingo Molnar Jan 26, 2009

x86: micro-optimize __raw_read_trylock()

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>

parent 7106a5ab

arch/x86/include/asm/spinlock.h

+1 −2

Original line number	Diff line number	Diff line
		@@ -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;