linux-kernel - Re: [patch 00/10] [RFC] SLUB patches for more functionality, performance and maintenance

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Date:	Mon, 9 Jul 2007 14:55:59 -0700 (PDT)
From:	Christoph Lameter <clameter@....com>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
cc:	Martin Bligh <mbligh@...igh.org>, Andi Kleen <andi@...stfloor.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [patch 00/10] [RFC] SLUB patches for more functionality,
 performance and maintenance

On Mon, 9 Jul 2007, Mathieu Desnoyers wrote:

> > >Okay the source for these numbers is in his paper for the OLS 2006: Volume 
> > >1 page 208-209? I do not see the exact number that you referred to there.
> > 
> 
> Hrm, the reference page number is wrong: it is in OLS 2006, Vol. 1 page
> 216 (section 4.5.2 Scalability). I originally pulled out the page number
> from my local paper copy. oops.

4.5.2 is on page 208 in my copy of the proceedings.

> > >He seems to be comparing spinlock acquire / release vs. cmpxchg. So I 
> > >guess you got your material from somewhere else?
> > >
> 
> I ran a test specifically for this paper where I got this result
> comparing the local irq enable/disable to local cmpxchg.

The numbers are pretty important and suggest that we can obtain 
a significant speed increase by avoid local irq disable enable in the slab 
allocator fast paths. Do you some more numbers? Any other publication that 
mentions these?

> Yep, I volountarily used the variant without lock prefix because the
> data is per cpu and I disable preemption.

local_cmpxchg generates this?

> Yes, preempt disabling or, eventually, the new thread migration
> disabling I just proposed as an RFC on LKML. (that would make -rt people
> happier)

Right.

> Sure, also note that the UP cmpxchg (see asm-$ARCH/local.h in 2.6.22) is
> faster on architectures like powerpc and MIPS where it is possible to
> remove some memory barriers.

UP cmpxchg meaning local_cmpxchg?

> See 2.6.22 Documentation/local_ops.txt for a thorough discussion. Don't
> hesitate ping me if you have more questions.

That is pretty thin and does not mention atomic_cmpxchg. You way want to 
expand on your ideas a bit.
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