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From: "Emilio G. Cota" <cota@braap.org>
Date: Tue, 19 Apr 2016 19:07:43 -0400
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Subject: [Qemu-devel] [PATCH v3 04/11] include/processor.h: define
 cpu_relax()
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To: QEMU Developers <qemu-devel@nongnu.org>, MTTCG Devel <mttcg@listserver.greensocs.com>
Cc: =?UTF-8?q?Alex=20Benn=C3=A9e?= <alex.bennee@linaro.org>, Paolo Bonzini <pbonzini@redhat.com>, Peter Crosthwaite <crosthwaite.peter@gmail.com>, Richard Henderson <rth@twiddle.net>, Peter Maydell <peter.maydell@linaro.org>, Sergey Fedorov <serge.fdrv@gmail.com>

Taken from the linux kernel.

Reviewed-by: Richard Henderson <rth@twiddle.net>
Signed-off-by: Emilio G. Cota <cota@braap.org>
---
 include/qemu/processor.h | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)
 create mode 100644 include/qemu/processor.h

diff --git a/include/qemu/processor.h b/include/qemu/processor.h
new file mode 100644
index 0000000..675a00a
--- /dev/null
+++ b/include/qemu/processor.h
@@ -0,0 +1,28 @@
+#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")
+#endif
+
+#ifdef __ia64__
+#define cpu_relax() asm volatile("hint @pause" ::: "memory")
+#endif
+
+#ifdef __aarch64__
+#define cpu_relax() asm volatile("yield" ::: "memory")
+#endif
+
+#if 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")
+#endif
+
+#ifndef cpu_relax
+#define cpu_relax() barrier()
+#endif
+
+#endif /* QEMU_PROCESSOR_H */
-- 
2.5.0