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Commit 335d7afb authored by Gerald Schaefer's avatar Gerald Schaefer Committed by Ingo Molnar
Browse files

mutexes, sched: Introduce arch_mutex_cpu_relax() 



The spinning mutex implementation uses cpu_relax() in busy loops as a
compiler barrier. Depending on the architecture, cpu_relax() may do more
than needed in this specific mutex spin loops. On System z we also give
up the time slice of the virtual cpu in cpu_relax(), which prevents
effective spinning on the mutex.

This patch replaces cpu_relax() in the spinning mutex code with
arch_mutex_cpu_relax(), which can be defined by each architecture that
selects HAVE_ARCH_MUTEX_CPU_RELAX. The default is still cpu_relax(), so
this patch should not affect other architectures than System z for now.

Signed-off-by: default avatarGerald Schaefer <gerald.schaefer@de.ibm.com>
Signed-off-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <1290437256.7455.4.camel@thinkpad>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 22a867d8

arch/Kconfig

+3 −0
Original line number Diff line number Diff line
@@ -175,4 +175,7 @@ config HAVE_PERF_EVENTS_NMI 
config HAVE_ARCH_JUMP_LABEL

	bool



config HAVE_ARCH_MUTEX_CPU_RELAX

	bool



source "kernel/gcov/Kconfig"

arch/s390/Kconfig

+1 −0
Original line number Diff line number Diff line
@@ -99,6 +99,7 @@ config S390 
	select HAVE_KERNEL_LZMA

	select HAVE_KERNEL_LZO

	select HAVE_GET_USER_PAGES_FAST

	select HAVE_ARCH_MUTEX_CPU_RELAX

	select ARCH_INLINE_SPIN_TRYLOCK

	select ARCH_INLINE_SPIN_TRYLOCK_BH

	select ARCH_INLINE_SPIN_LOCK

arch/s390/include/asm/mutex.h

+2 −0
Original line number Diff line number Diff line
@@ -7,3 +7,5 @@ 
 */



#include <asm-generic/mutex-dec.h>



#define arch_mutex_cpu_relax()	barrier()

include/linux/mutex.h

+4 −0
Original line number Diff line number Diff line
@@ -160,4 +160,8 @@ extern int mutex_trylock(struct mutex *lock); 
extern void mutex_unlock(struct mutex *lock);

extern int atomic_dec_and_mutex_lock(atomic_t *cnt, struct mutex *lock);



#ifndef CONFIG_HAVE_ARCH_MUTEX_CPU_RELAX

#define arch_mutex_cpu_relax()	cpu_relax()

#endif



#endif

kernel/mutex.c

+1 −1
Original line number Diff line number Diff line
@@ -199,7 +199,7 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass, 
		 * memory barriers as we'll eventually observe the right

		 * values at the cost of a few extra spins.

		 */

		cpu_relax();

		arch_mutex_cpu_relax();

	}

#endif

	spin_lock_mutex(&lock->wait_lock, flags);