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From: Sergey Fedorov <serge.fdrv@gmail.com>
Message-ID: <5748B3AD.4050304@gmail.com>
Date: Fri, 27 May 2016 23:53:01 +0300
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Subject: Re: [Qemu-devel] [PATCH v6 04/15] include/processor.h: define
 cpu_relax()
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To: "Emilio G. Cota" <cota@braap.org>, QEMU Developers <qemu-devel@nongnu.org>, MTTCG Devel <mttcg@listserver.greensocs.com>
Cc: =?UTF-8?Q?Alex_Benn=c3=a9e?= <alex.bennee@linaro.org>, Paolo Bonzini <pbonzini@redhat.com>, Richard Henderson <rth@twiddle.net>

On 25/05/16 04:13, Emilio G. Cota wrote:
> Taken from the linux kernel.
>
> Reviewed-by: Richard Henderson <rth@twiddle.net>
> Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
> Signed-off-by: Emilio G. Cota <cota@braap.org>
> ---
>  include/qemu/processor.h | 30 ++++++++++++++++++++++++++++++
>  1 file changed, 30 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..42bcc99
> --- /dev/null
> +++ b/include/qemu/processor.h
> @@ -0,0 +1,30 @@
> +/*
> + * Copyright (C) 2016, Emilio G. Cota <cota@braap.org>
> + *

If it's taken from the Linux kernel shouldn't it be attributed here?

> + * 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 */