linux-kernel - Re: SLUB performance regression vs SLAB

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Message-ID: <20071004183224.GA8641@linux.intel.com>
Date:	Thu, 4 Oct 2007 11:32:24 -0700
From:	Matthew Wilcox <willy@...ux.intel.com>
To:	Christoph Lameter <clameter@....com>
Cc:	Nick Piggin <nickpiggin@...oo.com.au>,
	Christoph Hellwig <hch@....de>, Mel Gorman <mel@...net.ie>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	David Chinner <dgc@....com>, Jens Axboe <jens.axboe@...cle.com>
Subject: Re: SLUB performance regression vs SLAB

On Thu, Oct 04, 2007 at 10:38:15AM -0700, Christoph Lameter wrote:
> On Thu, 4 Oct 2007, Matthew Wilcox wrote:
> 
> > So, on "a well-known OLTP benchmark which prohibits publishing absolute
> > numbers" and on an x86-64 system (I don't think exactly which model
> > is important), we're seeing *6.51%* performance loss on slub vs slab.
> > This is with a 2.6.23-rc3 kernel.  Tuning the boot parameters, as you've
> > asked for before (slub_min_order=2, slub_max_order=4, slub_min_objects=8)
> > gets back 0.38% of that.  It's still down 6.13% over slab.
> 
> Yeah the fastpath vs. slow path is not the issue as Siddha and I concluded 
> earlier. Seems that we are mainly seeing cacheline bouncing due to two 
> cpus accessing meta data in the same page struct. The patches in 
> MM that are scheduled to be merged for .24 address that issue. I 
> have repeatedly asked that these patches be tested. The patches were 
> posted months ago.

I just checked with the guys who did the test.  When I said -rc3, I
mis-spoke; this is 2.6.23-rc3 *plus* the patches which Suresh agreed to
test for you.
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