linux-kernel - Re: [patch 08/10] SLUB: Optional fast path using cmpxchg

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Date:	Tue, 30 Oct 2007 11:58:08 -0700 (PDT)
From:	Christoph Lameter <clameter@....com>
To:	Andrew Morton <akpm@...ux-foundation.org>
cc:	matthew@....cx, linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	penberg@...helsinki.fi,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	linux-arch@...r.kernel.org
Subject: Re: [patch 08/10] SLUB: Optional fast path using cmpxchg_local

On Tue, 30 Oct 2007, Andrew Morton wrote:

> Let's cc linux-arch: presumably other architectures can implement cpu-local
> cmpxchg and would see some benefit from doing so.

Matheiu had a whole series of cmpxchg_local patches. Ccing him too. I 
think he has some numbers for other architectures.

> The semantics are "atomic wrt interrutps on this cpu, not atomic wrt other
> cpus", yes?

Right.

> Do you have a feel for how useful it would be for arch maintainers to implement
> this?  IOW, is it worth their time?

That depends on the efficiency of a cmpxchg_local vs. the interrupt 
enable/ disable sequence on a particular arch. On x86 this yields about 
50% so it doubles the speed of the fastpath. On other architectures the 
cmpxchg is so slow that it is not worth it (ia64 f.e.)
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