netdev - Re: [PATCHv5 2/2] memory barrier: adding smp_mb__after

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Date:	Tue, 07 Jul 2009 17:23:18 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
CC:	Jiri Olsa <jolsa@...hat.com>, Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	fbl@...hat.com, nhorman@...hat.com, davem@...hat.com,
	htejun@...il.com, jarkao2@...il.com, oleg@...hat.com,
	davidel@...ilserver.org
Subject: Re: [PATCHv5 2/2] memory barrier: adding smp_mb__after_lock

Mathieu Desnoyers a écrit :

> But read_lock + smp_mb__after_lock + read_unlock is not well suited for
> powerpc, arm, mips and probably others where there is an explicit memory
> barrier at the end of the read lock primitive.
> 
> One thing that would be efficient for all architectures is to create a
> locking primitive that contains the smp_mb, e.g.:
> 
> read_lock_smp_mb()
> 
> which would act as a read_lock which does a full smp_mb after the lock
> is taken.
> 
> The naming may be a bit odd, better ideas are welcome.

I see your point now, thanks for your patience.

Jiri, I think your first patch can be applied (including the full smp_mb()),
 then we will optimize both for x86 and other arches, when all 
arch maintainers have a chance to change
"read_lock();smp_mb()" to a faster "read_lock_mb()" or something :)

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