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From: Richard Henderson <rth@twiddle.net>
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Date: Fri, 8 Apr 2016 11:40:25 -0700
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Subject: Re: [Qemu-devel] [PATCH v2 08/13] qemu-thread: optimize spin_lock
 for uncontended locks
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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:
>  static inline void qemu_spin_lock(QemuSpin *spin)
>  {
> -    do {
> +    while (atomic_xchg(&spin->value, true)) {
>          while (atomic_read(&spin->value)) {
>              cpu_relax();
>          }
> -    } while (atomic_xchg(&spin->value, true));
> +    }
>  }

And merge this one as well, please.  It's a good improvement, but there's
little point to keeping these separate.


r~