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Subject[PATCH 01/11] x86 rwsem: stay on fast path when count>0 in __up_write()
Date
When count>0 there is no need to take the call_rwsem_wake path.
If we did take that path, it would just return without doing anything
due to the active count not being zero.

Signed-off-by: Michel Lespinasse <walken@google.com>
Acked-by: David Howells <dhowells@redhat.com>
---
arch/x86/include/asm/rwsem.h | 5 ++---
1 files changed, 2 insertions(+), 3 deletions(-)

diff --git a/arch/x86/include/asm/rwsem.h b/arch/x86/include/asm/rwsem.h
index 606ede1..3fd1ed3 100644
--- a/arch/x86/include/asm/rwsem.h
+++ b/arch/x86/include/asm/rwsem.h
@@ -216,9 +216,8 @@ static inline void __up_write(struct rw_semaphore *sem)
rwsem_count_t tmp;
asm volatile("# beginning __up_write\n\t"
LOCK_PREFIX " xadd %1,(%2)\n\t"
- /* tries to transition
- 0xffff0001 -> 0x00000000 */
- " jz 1f\n"
+ /* substracts 0xffff0001, returns the old value */
+ " jns 1f\n\t"
" call call_rwsem_wake\n"
"1:\n\t"
"# ending __up_write\n"
--
1.7.0.1


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