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From: Richard Henderson <rth@twiddle.net>
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Date: Fri, 8 Apr 2016 11:33:17 -0700
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Subject: Re: [Qemu-devel] [PATCH v2 05/13] 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@greensocs.com>
Cc: =?UTF-8?Q?Alex_Benn=c3=a9e?= <alex.bennee@linaro.org>, Paolo Bonzini <pbonzini@redhat.com>, Peter Crosthwaite <crosthwaite.peter@gmail.com>, Peter Maydell <peter.maydell@linaro.org>, Sergey Fedorov <serge.fdrv@gmail.com>

On 04/07/2016 10:32 AM, Emilio G. Cota wrote:
> Taken from the linux kernel.
> 
> 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

Reviewed-by: Richard Henderson  <rth@twiddle.net>


> +#if defined(__i386__) || defined(__x86_64__)
> +#define cpu_relax() asm volatile("rep; nop" ::: "memory")
> +#endif

Not that it matters much, but for the record there's an ICC inspired builtin in
<xmmintrin.h> for this: _mm_pause().  But so long as we're always using gcc or
clang, that's probably just an extra dependency to worry about.


r~