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

From: Mathieu Desnoyers <[email-masked]>
Date: Fri, 3 Jul 2009 11:47:00 -0400

* Eric Dumazet ([email-masked]) wrote:
> 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 ?
> 

I think he meant RCU.

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

At least PowerPC, MIPS, recent ARM, alpha.

Mathieu

-- 
Mathieu Desnoyers
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