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

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Message-Id: <1171326305.19842.36.camel@localhost.localdomain>
Date:	Tue, 13 Feb 2007 11:25:05 +1100
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Jens Axboe <jens.axboe@...cle.com>
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, 2007-02-12 at 16:01 +0100, Jens Axboe wrote:
> On Mon, Feb 12 2007, Rusty Russell wrote:
> > 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 :-)

*cough* I deliberately leave these low hanging fruit in lguest to
encourage people to hack on it.  Really.  *cough*

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

The question is whether the guest or host should queue.  If you have
multiple guests sharing a disk in the hose, I would think that the host
is better off queuing.  And this would seem to be the common case.

On my todo list is:
1) Implement write barriers, (-> fsync in the host)
2) Make the host userspace program (lguest) async rather than blocking,
3) Allow multiple outstanding requests.

Then it should be useful for other hypervisors.

Cheers!
Rusty.

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