linux-kernel - Re: Major regression on hackbench with SLUB (more numbers)

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Message-ID: <Pine.LNX.4.64.0712211350540.3795@schroedinger.engr.sgi.com>
Date:	Fri, 21 Dec 2007 13:56:11 -0800 (PST)
From:	Christoph Lameter <clameter@....com>
To:	Ingo Molnar <mingo@...e.hu>
cc:	Steven Rostedt <rostedt@...dmis.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Christoph Hellwig <hch@...radead.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>
Subject: Re: Major regression on hackbench with SLUB (more numbers)

On Fri, 21 Dec 2007, Ingo Molnar wrote:

> > There are patches pending to address these issues. AFAICT Intel is 
> > testing if the regression is still there. There is no way for me to 
> > verify what is going on there and there is the constant difficulty of 
> > getting detailed information about what is going on at Intel. Every 
> > couple of month I get a result from that test. Its a really crappy 
> > situation where a lot of confusing information is passed around.
> 
> of course there is a way to find out, and that's why i mailed you: fix 
> the hackbench regression and i'm quite sure you'll improve the TPC-C 
> numbers as well. It shows the same kind of overhead in the profile and 
> takes just a few seconds to run. Are your pending SLUB patches in 
> 2.6.24-rc5-mm1 already?

The tests that I wrote emulate the test behavior that was described to me 
by me.

The fixes in 2.6.24-rc5-mm1 improved those numbers. See 
http://lkml.org/lkml/2007/10/27/245 which I quoted earlier to you. 
However, I have no TPC-C setup here and from what I hear it takes weeks to 
run and requires a large support team for tuning.

You can find the slab test suite for that at

http://git.kernel.org/?p=linux/kernel/git/christoph/vm.git;a=shortlog;h=tests

AFAICT the fixes in 2.6.25-rc5-mm1 result in double the alloc performance 
(fastpath) of SLAB.

There are fixes that are not merged yet (the cpu alloc patchset) that 
seem to make that factor 3 because we can use the segment register to 
avoid per cpu array lookups in the fast path.
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