From 0b2fcfdb8b4e7e379192f24ea2203163ddf5df1d Mon Sep 17 00:00:00 2001 From: Nick Piggin Date: Thu, 23 Mar 2006 03:01:02 -0800 Subject: [PATCH] atomic: add_unless cmpxchg optimise Without branch hints, the very unlikely chance of the loop repeating due to cmpxchg failure is unrolled with gcc-4 that I have tested. Improve this for architectures with a native cas/cmpxchg. llsc archs should try to implement this natively. Signed-off-by: Nick Piggin Cc: Andi Kleen Cc: Martin Schwidefsky Cc: Heiko Carstens Cc: "David S. Miller" Cc: Roman Zippel Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/asm-sparc64/atomic.h | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-) (limited to 'include/asm-sparc64') diff --git a/include/asm-sparc64/atomic.h b/include/asm-sparc64/atomic.h index 25256bdc8aae..468eb48d8142 100644 --- a/include/asm-sparc64/atomic.h +++ b/include/asm-sparc64/atomic.h @@ -78,9 +78,15 @@ extern int atomic64_sub_ret(int, atomic64_t *); ({ \ int c, old; \ c = atomic_read(v); \ - while (c != (u) && (old = atomic_cmpxchg((v), c, c + (a))) != c) \ + for (;;) { \ + if (unlikely(c == (u))) \ + break; \ + old = atomic_cmpxchg((v), c, c + (a)); \ + if (likely(old == c)) \ + break; \ c = old; \ - c != (u); \ + } \ + likely(c != (u)); \ }) #define atomic_inc_not_zero(v) atomic_add_unless((v), 1, 0) -- cgit v1.2.3-58-ga151