Commit a751bd85 authored Jul 20, 2010 by Michel Lespinasse Committed by H. Peter Anvin Jul 20, 2010

x86, rwsem: Stay on fast path when count > 0 in __up_write()



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>
LKML-Reference: <201007202219.o6KMJj9x021042@imap1.linux-foundation.org>
Acked-by: David Howells <dhowells@redhat.com>
Cc: Mike Waychison <mikew@google.com>
Cc: Suleiman Souhlal <suleiman@google.com>
Cc: Ying Han <yinghan@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>

parent e0959371

arch/x86/include/asm/rwsem.h

+2 −3

Original line number	Diff line number	Diff line
		@@ -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"
		/* subtracts 0xffff0001, returns the old value */
		" jns 1f\n\t"
		" call call_rwsem_wake\n"
		"1:\n\t"
		"# ending __up_write\n"