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include/processor.h: define cpu_relax()

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Taken from the linux kernel.

Reviewed-by: Sergey Fedorov <sergey.fedorov@linaro.org>
Reviewed-by: Richard Henderson <rth@twiddle.net>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Emilio G. Cota <cota@braap.org>
Message-Id: <1465412133-3029-5-git-send-email-cota@braap.org>
Signed-off-by: Richard Henderson <rth@twiddle.net>
This commit is contained in:
Emilio G. Cota 2016-06-08 14:55:22 -04:00 committed by Richard Henderson
parent 03719e44b6
commit 462cda505f
1 changed files with 30 additions and 0 deletions
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30
include/qemu/processor.h Normal file
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/*
* Copyright (C) 2016, Emilio G. Cota <cota@braap.org>
*
* License: GNU GPL, version 2.
* See the COPYING file in the top-level directory.
*/
#ifndef QEMU_PROCESSOR_H
#define QEMU_PROCESSOR_H
#include "qemu/atomic.h"
#if defined(__i386__) || defined(__x86_64__)
# define cpu_relax() asm volatile("rep; nop" ::: "memory")
#elif defined(__ia64__)
# define cpu_relax() asm volatile("hint @pause" ::: "memory")
#elif defined(__aarch64__)
# define cpu_relax() asm volatile("yield" ::: "memory")
#elif defined(__powerpc64__)
/* set Hardware Multi-Threading (HMT) priority to low; then back to medium */
# define cpu_relax() asm volatile("or 1, 1, 1;" \
"or 2, 2, 2;" ::: "memory")
#else
# define cpu_relax() barrier()
#endif
#endif /* QEMU_PROCESSOR_H */