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

From: Paolo Bonzini
Subject: Re: [Qemu-devel] [PATCH v5 05/18] atomics: add atomic_test_and_set_acquire
Date: Tue, 17 May 2016 19:08:26 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.0

On 17/05/2016 18:47, 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.

That will be fixed soon by adding smp_mb_acquire() and smp_mb_release(). :)


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