Subject: Re: [PATCHv5 2/2] memory barrier: adding smp_mb__after_lock

From: Eric Dumazet <[email-masked]>
Date: Fri, 03 Jul 2009 17:37:31 +0200

Herbert Xu a écrit :
> Mathieu Desnoyers <[email-masked]> wrote:
>> Why don't we create a read_lock without acquire semantic instead (e.g.
>> read_lock_nomb(), or something with a better name like __read_lock()) ?
>> On architectures where memory barriers are needed to provide the acquire
>> semantic, it would be faster to do :
>>
>> __read_lock();
>> smp_mb();
>>
>> than :
>>
>> read_lock(); <- e.g. lwsync + isync or something like that
>> smp_mb(); <- full sync.
> 
> Hmm, why do we even care when read_lock should just die?
> 
> Cheers,

+1 :)

Do you mean using a spinlock instead or what ?

Also, how many arches are able to have a true __read_lock()
(or __spin_lock() if that matters), without acquire semantic ?