linux-kernel - RE: [patch] speed up single bio

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Date:	Thu, 7 Dec 2006 13:52:59 -0800
From:	"Chen, Kenneth W" <kenneth.w.chen@...el.com>
To:	"'Nate Diller'" <nate.diller@...il.com>
Cc:	"Jens Axboe" <jens.axboe@...cle.com>,
	"linux-kernel" <linux-kernel@...r.kernel.org>
Subject: RE: [patch] speed up single bio_vec allocation

Nate Diller wrote on Thursday, December 07, 2006 1:46 PM
> the current code is straightforward and obviously correct.  you want
> to make the alloc/dealloc paths more complex, by special-casing for an
> arbitrary limit of "small" I/O, AFAICT.  of *course* you can expect
> less overhead when you're doing one large I/O vs. two small ones,
> that's the whole reason we have all this code to try to coalesce
> contiguous I/O, do readahead, swap page clustering, etc.  we *want*
> more complexity if it will get us bigger I/Os.  I don't see why we
> want more complexity to reduce the *inherent* penalty of doing smaller
> ones.

You should check out the latest proposal from Jens Axboe which treats
all biovec size the same and stuff it along with struct bio.  I think
it is a better approach than my first cut of special casing 1 segment
biovec.  His patch will speed up all sized I/O.

- Ken
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