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mutexes, sched: 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
2010-11-22 15:47:36 +01:00
committed by Ingo Molnar
parent 22a867d817
commit 335d7afbfb
6 changed files with 13 additions and 2 deletions
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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"
@@ -3888,7 +3889,7 @@ 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;