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From: Nick Piggin <npiggin@suse.de>
Subject: Re: [PATCH 03/13] scsi: unify allocation of scsi command and sense buffer
Date: Mon, 25 May 2009 13:32:51 +0200
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Cc: Jens Axboe <jens.axboe@oracle.com>, linux-kernel@vger.kernel.org,
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To: Pekka Enberg <penberg@cs.helsinki.fi>
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On Mon, May 25, 2009 at 11:15:42AM +0300, Pekka Enberg wrote:
> On Mon, May 25, 2009 at 10:30 AM, Jens Axboe <jens.axboe@oracle.com> wrote:
> > Fold the sense buffer into the command, thereby eliminating a slab
> > allocation and free per command.
> >
> > Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
> 
> Interesting. I wonder how this affects the SLAB vs. SLUB regression
> people are seeing on high end machines in OLTP benchmarks.

It could improve it. I think these (bios, requests, commands etc) allocations
are what SLUB has trouble with in that workload, so eliminating one of them
should help it. I guess it will help the other allocators as well, but maybe
a smaller relative improvement?