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Date: Thu, 23 Oct 2008 09:02:08 +0200
From: Nick Piggin <npiggin@suse.de>
To: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Subject: Re: [patch] mutex: optimise generic mutex implementations
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Cc: linux-arch@vger.kernel.org, linuxppc-dev@ozlabs.org,
	Ingo Molnar <mingo@elte.hu>, paulus@samba.org,
	Peter Zijlstra <a.p.zijlstra@chello.nl>
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On Thu, Oct 23, 2008 at 03:43:58PM +1100, Benjamin Herrenschmidt wrote:
> On Wed, 2008-10-22 at 17:59 +0200, Ingo Molnar wrote:
> > * Nick Piggin <npiggin@suse.de> wrote:
> > 
> > > Speed up generic mutex implementations.
> > > 
> > > - atomic operations which both modify the variable and return something imply
> > >   full smp memory barriers before and after the memory operations involved
> > >   (failing atomic_cmpxchg, atomic_add_unless, etc don't imply a barrier because
> > >   they don't modify the target). See Documentation/atomic_ops.txt.
> > >   So remove extra barriers and branches.
> > >   
> > > - All architectures support atomic_cmpxchg. This has no relation to
> > >   __HAVE_ARCH_CMPXCHG. We can just take the atomic_cmpxchg path unconditionally
> > > 
> > > This reduces a simple single threaded fastpath lock+unlock test from 590 cycles
> > > to 203 cycles on a ppc970 system.
> > > 
> > > Signed-off-by: Nick Piggin <npiggin@suse.de>
> > 
> > no objections here. Lets merge these two patches via the ppc tree, so 
> > that it gets testing on real hardware as well?
> > 
> > Acked-by: Ingo Molnar <mingo@elte.hu>
> 
> Allright but in that case it will be after -rc1 unless I manage to sneak
> something in tomorrow before linux closes the merge window.
> 
> I can't get an update today.

Fine with me.

Thanks,
Nick