linux-kernel - Re: request->ioprio

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Date:	Thu, 7 Aug 2008 06:33:05 +1000
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Fernando Luis Vázquez Cao 
	<fernando@....ntt.co.jp>
Cc:	Jens Axboe <jens.axboe@...cle.com>, linux-kernel@...r.kernel.org
Subject: Re: request->ioprio

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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