linux-kernel - Re: SLUB: Avoid atomic operation for slab

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Message-ID: <Pine.LNX.4.64.0710181858240.4685@schroedinger.engr.sgi.com>
Date:	Thu, 18 Oct 2007 19:01:52 -0700 (PDT)
From:	Christoph Lameter <clameter@....com>
To:	Nick Piggin <nickpiggin@...oo.com.au>
cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	akpm@...ux-foundation.org, linux-mm@...ck.org
Subject: Re: SLUB: Avoid atomic operation for slab_unlock

On Fri, 19 Oct 2007, Nick Piggin wrote:

> > Yes that is what I attempted to do with the write barrier. To my knowledge
> > there are no reads that could bleed out and I wanted to avoid a full fence
> > instruction there.
> 
> Oh, OK. Bit risky ;) You might be right, but anyway I think it
> should be just as fast with the optimised bit_unlock on most
> architectures.

How expensive is the fence? An store with release semantics would be safer 
and okay for IA64.

> Which reminds me, it would be interesting to test the ia64
> implementation I did. For the non-atomic unlock, I'm actually
> doing an atomic operation there so that it can use the release
> barrier rather than the mf. Maybe it's faster the other way around
> though? Will be useful to test with something that isn't a trivial
> loop, so the slub case would be a good benchmark.

Lets avoid mf (too expensive) and just use a store with release semantics.

Where can I find your patchset? I looked through lkml but did not see it.
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