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authorNick Piggin <npiggin@suse.de>2006-03-23 03:01:02 -0800
committerLinus Torvalds <torvalds@g5.osdl.org>2006-03-23 07:38:17 -0800
commit0b2fcfdb8b4e7e379192f24ea2203163ddf5df1d (patch)
tree1f3995e41ab12ff76e737389e0b59a40c0c73668 /include/asm-i386
parent713729e8b993cb880225e2ced50a3f5ac05c2b3f (diff)
[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 <npiggin@suse.de> Cc: Andi Kleen <ak@muc.de> Cc: Martin Schwidefsky <schwidefsky@de.ibm.com> Cc: Heiko Carstens <heiko.carstens@de.ibm.com> Cc: "David S. Miller" <davem@davemloft.net> Cc: Roman Zippel <zippel@linux-m68k.org> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Diffstat (limited to 'include/asm-i386')
-rw-r--r--include/asm-i386/atomic.h8
1 files changed, 7 insertions, 1 deletions
diff --git a/include/asm-i386/atomic.h b/include/asm-i386/atomic.h
index 78b0032d1f2..22d80ece95c 100644
--- a/include/asm-i386/atomic.h
+++ b/include/asm-i386/atomic.h
@@ -225,8 +225,14 @@ static __inline__ int atomic_sub_return(int i, atomic_t *v)
({ \
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); \
})
#define atomic_inc_not_zero(v) atomic_add_unless((v), 1, 0)