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From: Alex =?utf-8?Q?Benn=C3=A9e?= <alex.bennee@linaro.org>
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Date: Fri, 22 Apr 2016 10:35:35 +0100
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Subject: Re: [Qemu-devel] [PATCH v3 04/11] include/processor.h: define
 cpu_relax()
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To: "Emilio G. Cota" <cota@braap.org>
Cc: QEMU Developers <qemu-devel@nongnu.org>, MTTCG Devel <mttcg@listserver.greensocs.com>, 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>


Emilio G. Cota <cota@braap.org> writes:

> Taken from the linux kernel.
>
> Reviewed-by: Richard Henderson <rth@twiddle.net>
> Signed-off-by: Emilio G. Cota <cota@braap.org>

License header notwithstanding:


Reviewed-by: Alex Bennée <alex.bennee@linaro.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 */


--
Alex Bennée