Date: Fri, 3 Jul 2009 11:47:00 -0400
From: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
To: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Herbert Xu <herbert@gondor.apana.org.au>, mingo@elte.hu, jolsa@redhat.com,
       a.p.zijlstra@chello.nl, netdev@vger.kernel.org,
       linux-kernel@vger.kernel.org, fbl@redhat.com, nhorman@redhat.com,
       davem@redhat.com, htejun@gmail.com, jarkao2@gmail.com, oleg@redhat.com,
       davidel@xmailserver.org, Paul.McKenney@us.ibm.com
Subject: Re: [PATCHv5 2/2] memory barrier: adding smp_mb__after_lock
Message-ID: <20090703154700.GD10256@Krystal>
References: <20090703152951.GA28837@gondor.apana.org.au> <4A4E25BB.8060408@gmail.com>
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* Eric Dumazet (eric.dumazet@gmail.com) wrote:
> Herbert Xu a ?crit :
> > 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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