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[S390] mutex: Introduce arch_mutex_cpu_relax()

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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: Gerald Schaefer <gerald.schaefer@de.ibm.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <1290437256.7455.4.camel@thinkpad>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Gerald Schaefer 2011-01-05 12:48:14 +01:00 committed by Martin Schwidefsky
parent c03017544e
commit 34b133f8e9
6 changed files with 13 additions and 2 deletions
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3
arch/Kconfig
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@ -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"

1
arch/s390/Kconfig
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@ -87,6 +87,7 @@ 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

2
arch/s390/include/asm/mutex.h
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@ -7,3 +7,5 @@
*/
#include <asm-generic/mutex-dec.h>
#define arch_mutex_cpu_relax() barrier()

4
include/linux/mutex.h
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@ -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

2
kernel/mutex.c
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@ -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);

3
kernel/sched.c
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@ -75,6 +75,7 @@
#include <asm/tlb.h>
#include <asm/irq_regs.h>
#include <asm/mutex.h>
#include "sched_cpupri.h"
#include "workqueue_sched.h"
@ -4214,7 +4215,7 @@ int mutex_spin_on_owner(struct mutex *lock, struct thread_info *owner)
if (task_thread_info(rq->curr) != owner || need_resched())
return 0;
cpu_relax();
arch_mutex_cpu_relax();
}
return 1;