linux-kernel - Re: [PATCH 7/8] lguest: trivial guest block driver

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Message-ID: <20070212150125.GM3999@kernel.dk>
Date:	Mon, 12 Feb 2007 16:01:25 +0100
From:	Jens Axboe <jens.axboe@...cle.com>
To:	Rusty Russell <rusty@...tcorp.com.au>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	lkml - Kernel Mailing List <linux-kernel@...r.kernel.org>,
	virtualization <virtualization@...ts.osdl.org>
Subject: Re: [PATCH 7/8] lguest: trivial guest block driver

On Mon, Feb 12 2007, Rusty Russell wrote:
> On Mon, 2007-02-12 at 06:32 +0100, Jens Axboe wrote:
> > On Mon, Feb 12 2007, Rusty Russell wrote:
> > > On Mon, 2007-02-12 at 05:43 +0100, Jens Axboe wrote:
> > > > Here you map the entire request (lets call that segment A..Z), but
> > > > end_request() only completes the first chunk of the request. So
> > > > elv_next_request() will retrieve the same request again, and you'll then
> > > > map B..Z and repeat that transfer. So unless I'm missing some other part
> > > > here (just read it over quickly), you are re-doing large parts of a
> > > > merged request several times.
> 
> virtbench before:
> 	Time to read from disk (256 kB): 18654562 nsec
> After:
> 	Time to read from disk (256 kB): 8018468 nsec
> 
> Thanks Jens!!

My pleasure, it's not often you get to make that big a performance
improvement with just a little few lines of change :-)

I guess you'll take changes to make this driver queuing as well? It's
pretty important for good guest io performance as well.

-- 
Jens Axboe

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