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Re: [Qemu-devel] [PATCH v5 07/18] qemu-thread: add simple test-and-set s

From: Sergey Fedorov
Subject: Re: [Qemu-devel] [PATCH v5 07/18] qemu-thread: add simple test-and-set spinlock
Date: Wed, 18 May 2016 17:18:50 +0300
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.7.2

On 18/05/16 03:28, Emilio G. Cota wrote:
> On Tue, May 17, 2016 at 23:20:11 +0300, Sergey Fedorov wrote:
>> On 17/05/16 23:04, Emilio G. Cota wrote:
> (snip)
>>> +/*
>>> + * We might we tempted to use __atomic_test_and_set with __ATOMIC_ACQUIRE;
>>> + * however, the documentation explicitly says that we should only pass
>>> + * a boolean to it, so we use __sync_lock_test_and_set, which doesn't
>>> + * have this limitation, and is documented to have acquire semantics.
>>> + */
>>> +#define atomic_test_and_set_acquire(ptr) __sync_lock_test_and_set(ptr, 
>>> true)
>> So you are going to stick to *legacy* built-ins?
> Why not? AFAIK the reason to avoid __sync primitives is that in most cases
> they include barriers that callers might not necessarily need; __atomic's
> allow for finer tuning, which is in general a good thing. However,
> __sync_test_and_set has the exact semantics we need, without the limitations
> documented for __atomic_test_and_set; so why not use it?

So it should be okay as long as the legacy build-ins are supported.

Kind regards,

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