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From: Sergey Fedorov <serge.fdrv@gmail.com>
Message-ID: <573B4B20.8010601@gmail.com>
Date: Tue, 17 May 2016 19:47:28 +0300
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Subject: Re: [Qemu-devel] [PATCH v5 05/18] atomics: add
 atomic_test_and_set_acquire
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To: Paolo Bonzini <pbonzini@redhat.com>, "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>, Peter Crosthwaite <crosthwaite.peter@gmail.com>, Richard Henderson <rth@twiddle.net>

On 17/05/16 19:23, Paolo Bonzini wrote:
>
> On 17/05/2016 18:15, Sergey Fedorov wrote:
>> On 14/05/16 06:34, Emilio G. Cota wrote:
>>> This new helper expands to __atomic_test_and_set with acquire semantics
>>> where available; otherwise it expands to __sync_test_and_set, which
>>> has acquire semantics.
>> Why don't also add atomic_clear_release() for completeness?
> The previous patch adds atomic_set_release.

Yes, but it would take the advantage of __sync_lock_release() being just
a release barrier rather than a full barrier of smp_mb() in
atomic_set_release(). But that's only the case for legacy __sync
built-ins (before GCC 4.7.0), though.

Kind regards,
Sergey