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

Mathieu Desnoyers
2009-07-03T15:52:25Z

* Eric Dumazet (eric.dumazet@gmail.com) wrote:
> Herbert Xu a écrit :
> > Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca> 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

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Mathieu Desnoyers
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