Commit cc189d25 authored Apr 17, 2013 by Waiman Long Committed by Ingo Molnar Apr 19, 2013

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>

parent 2bd2c92c

arch/x86/include/asm/mutex.h

+0 −10

Original line number	Diff line number	Diff line
		@@ -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

kernel/mutex.c

+2 −7

Original line number	Diff line number	Diff line
		@@ -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)

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