diff options
| author | Nick Piggin <npiggin@suse.de> | 2008-10-21 10:59:15 +0200 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2008-10-23 09:18:20 -0700 |
| commit | a8ddac7e53e89cb877965097d05adfeb1c91def3 (patch) | |
| tree | db4ee686e50f7fb57b0cef20e0a8e7f06151e317 /include/asm-generic/mutex-xchg.h | |
| parent | 5a439c565799cb8d290d71ce375e86be64d43a4b (diff) | |
mutex: speed up generic mutex implementations
- atomic operations which both modify the variable and return something imply
full smp memory barriers before and after the memory operations involved
(failing atomic_cmpxchg, atomic_add_unless, etc don't imply a barrier because
they don't modify the target). See Documentation/atomic_ops.txt.
So remove extra barriers and branches.
- All architectures support atomic_cmpxchg. This has no relation to
__HAVE_ARCH_CMPXCHG. We can just take the atomic_cmpxchg path unconditionally
This reduces a simple single threaded fastpath lock+unlock test from 590 cycles
to 203 cycles on a ppc970 system.
Signed-off-by: Nick Piggin <npiggin@suse.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'include/asm-generic/mutex-xchg.h')
| -rw-r--r-- | include/asm-generic/mutex-xchg.h | 9 |
1 files changed, 1 insertions, 8 deletions
diff --git a/include/asm-generic/mutex-xchg.h b/include/asm-generic/mutex-xchg.h index 7b9cd2cbfeb..580a6d35c70 100644 --- a/include/asm-generic/mutex-xchg.h +++ b/include/asm-generic/mutex-xchg.h @@ -27,8 +27,6 @@ __mutex_fastpath_lock(atomic_t *count, void (*fail_fn)(atomic_t *)) { if (unlikely(atomic_xchg(count, 0) != 1)) fail_fn(count); - else - smp_mb(); } /** @@ -46,10 +44,7 @@ __mutex_fastpath_lock_retval(atomic_t *count, int (*fail_fn)(atomic_t *)) { if (unlikely(atomic_xchg(count, 0) != 1)) return fail_fn(count); - else { - smp_mb(); - return 0; - } + return 0; } /** @@ -67,7 +62,6 @@ __mutex_fastpath_lock_retval(atomic_t *count, int (*fail_fn)(atomic_t *)) static inline void __mutex_fastpath_unlock(atomic_t *count, void (*fail_fn)(atomic_t *)) { - smp_mb(); if (unlikely(atomic_xchg(count, 1) != 0)) fail_fn(count); } @@ -110,7 +104,6 @@ __mutex_fastpath_trylock(atomic_t *count, int (*fail_fn)(atomic_t *)) if (prev < 0) prev = 0; } - smp_mb(); return prev; } |