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mutex: Back out architecture specific check for negative mutex count 

Linus suggested that probably all the supported architectures can
allow a negative mutex count without incorrect behavior, so we can
then back out the architecture specific change and allow the
mutex count to go to any negative number. That should further
reduce contention for non-x86 architecture.

Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Waiman Long <Waiman.Long@hp.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Chandramouleeswaran Aswin <aswin@hp.com>
Cc: Davidlohr Bueso <davidlohr.bueso@hp.com>
Cc: Norton Scott J <scott.norton@hp.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Dave Jones <davej@redhat.com>
Cc: Clark Williams <williams@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1366226594-5506-5-git-send-email-Waiman.Long@hp.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Waiman Long 2013-04-17 15:23:14 -04:00 committed by Ingo Molnar
parent 2bd2c92cf0
commit cc189d2513
2 changed files with 2 additions and 17 deletions
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10
arch/x86/include/asm/mutex.h
View File

@ -3,13 +3,3 @@
#else
# include <asm/mutex_64.h>
#endif
#ifndef __ASM_MUTEX_H
#define __ASM_MUTEX_H
/*
* For the x86 architecture, it allows any negative number (besides -1) in
* the mutex count to indicate that some other threads are waiting on the
* mutex.
*/
#define __ARCH_ALLOW_ANY_NEGATIVE_MUTEX_COUNT 1
#endif

9
kernel/mutex.c
View File

@ -38,15 +38,10 @@
#endif
/*
* A mutex count of -1 indicates that waiters are sleeping waiting for the
* mutex. Some architectures can allow any negative number, not just -1, for
* this purpose.
* A negative mutex count indicates that waiters are sleeping waiting for the
* mutex.
*/
#ifdef __ARCH_ALLOW_ANY_NEGATIVE_MUTEX_COUNT
#define MUTEX_SHOW_NO_WAITER(mutex) (atomic_read(&(mutex)->count) >= 0)
#else
#define MUTEX_SHOW_NO_WAITER(mutex) (atomic_read(&(mutex)->count) != -1)
#endif
void
__mutex_init(struct mutex *lock, const char *name, struct lock_class_key *key)