tree 462da9df24831e825deca5987e0fd283034cdfde
parent c03017544e3b2e60aa3c8ae451fac01595f1bf11
author Gerald Schaefer <gerald.schaefer@de.ibm.com> 1294228094 +0100
committer Martin Schwidefsky <sky@mschwide.boeblingen.de.ibm.com> 1294228051 +0100

[S390] mutex: 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: 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>