From: Rusty Russell <rusty@rustcorp.com.au>
To: Fernando Luis =?utf-8?q?V=C3=A1zquez_Cao?= 
	<fernando@oss.ntt.co.jp>
Subject: Re: request->ioprio
Date: Thu, 7 Aug 2008 06:33:05 +1000
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Cc: Jens Axboe <jens.axboe@oracle.com>, linux-kernel@vger.kernel.org
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On Wednesday 06 August 2008 19:16:36 Fernando Luis Vázquez Cao wrote:
> Hi Jens, Rusty,

Hi Fernando,

> Trying to implement i/o tracking all the way up to the page cache (so
> that cfq and the future cgroup-based I/O controllers can schedule
> buffered I/O properly) I noticed that struct request's ioprio is
> initialized but never used for I/O scheduling purposes. Indeed there
> seems to be one single user of this member: virtio_blk.

Hey, do I win a prize? :)

> Virtio uses 
> struct request's ioprio in the request() function of the virtio block
> driver, which just copies the ioprio value to the output header of
> virtblk_req.

Yes, we pass it through to the host, in the assumption they might want to use 
it to schedule our I/Os relative to each other.

I'm a little surprised noone else uses it, but I'm sure they will...
Rusty.
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