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Re: [Qemu-devel] [PATCH v5 05/18] atomics: add atomic_test_and_set_acqui

From: Sergey Fedorov
Subject: Re: [Qemu-devel] [PATCH v5 05/18] atomics: add atomic_test_and_set_acquire
Date: Tue, 17 May 2016 19:47:28 +0300
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.7.2

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,

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