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authorNick Piggin <npiggin@suse.de>2006-03-23 06:01:02 -0500
committerLinus Torvalds <torvalds@g5.osdl.org>2006-03-23 10:38:17 -0500
commit0b2fcfdb8b4e7e379192f24ea2203163ddf5df1d (patch)
tree1f3995e41ab12ff76e737389e0b59a40c0c73668 /include/asm-x86_64
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-x86_64')
-rw-r--r--include/asm-x86_64/atomic.h8
1 files changed, 7 insertions, 1 deletions
diff --git a/include/asm-x86_64/atomic.h b/include/asm-x86_64/atomic.h
index 4b5cd553e772..cecbf7baa6aa 100644
--- a/include/asm-x86_64/atomic.h
+++ b/include/asm-x86_64/atomic.h
@@ -405,8 +405,14 @@ static __inline__ long atomic64_sub_return(long i, atomic64_t *v)
405({ \ 405({ \
406 int c, old; \ 406 int c, old; \
407 c = atomic_read(v); \ 407 c = atomic_read(v); \
408 while (c != (u) && (old = atomic_cmpxchg((v), c, c + (a))) != c) \ 408 for (;;) { \
409 if (unlikely(c == (u))) \
410 break; \
411 old = atomic_cmpxchg((v), c, c + (a)); \
412 if (likely(old == c)) \
413 break; \
409 c = old; \ 414 c = old; \
415 } \
410 c != (u); \ 416 c != (u); \
411}) 417})
412#define atomic_inc_not_zero(v) atomic_add_unless((v), 1, 0) 418#define atomic_inc_not_zero(v) atomic_add_unless((v), 1, 0)