linux-kernel - Re: SLUB performance regression vs SLAB

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Message-ID: <20071005123953.GS5711@kernel.dk>
Date:	Fri, 5 Oct 2007 14:39:53 +0200
From:	Jens Axboe <jens.axboe@...cle.com>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Pekka Enberg <penberg@...helsinki.fi>, David Chinner <dgc@....com>,
	David Miller <davem@...emloft.net>, cebbert@...hat.com,
	willy@...ux.intel.com, clameter@....com, nickpiggin@...oo.com.au,
	hch@....de, mel@...net.ie, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, suresh.b.siddha@...el.com
Subject: Re: SLUB performance regression vs SLAB

On Fri, Oct 05 2007, Andi Kleen wrote:
> Jens Axboe <jens.axboe@...cle.com> writes:
> > 
> > Writing a small test module to exercise slub/slab in various ways
> > (allocating from all cpus freeing from one, as described) should not be
> > too hard. Perhaps that would be enough to find this performance
> > discrepancy between slab and slub?
> 
> You could simulate that by just sending packets using unix sockets
> between threads bound to different CPUs. Sending a packet allocates;
> receiving deallocates.

Sure, there are a host of ways to accomplish the same thing.

> But it's not clear that will really simulate the cache bounce
> environment of the database test. I don't think all passing of data
> between CPUs using slub objects is slow.

It might not, it might. The point is trying to isolate the problem and
making a simple test case that could be used to reproduce it, so that
Christoph (or someone else) can easily fix it.

-- 
Jens Axboe

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