linux-kernel - Re: request->ioprio

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Date:	Wed, 6 Aug 2008 10:22:30 -0700
From:	Divyesh Shah <dpshah@...gle.com>
To:	Fernando Luis Vázquez Cao 
	<fernando@....ntt.co.jp>
Cc:	Jens Axboe <jens.axboe@...cle.com>, rusty@...tcorp.com.au,
	linux-kernel@...r.kernel.org
Subject: Re: request->ioprio


On Aug 6, 2008, at 2:32 AM, Fernando Luis Vázquez Cao wrote:

> (CCing LKML)
>
> Hi Jens, Rusty,
>
> 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. 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.
>
> Is this the intended use of struct request's ioprio? Is it OK for  
> device
> drivers to use it? If the answer two the previous to questions is no I
> would like to send some clean-up patches.

Naveen Gupta sent a priority-based anticipatory IO scheduler patchset  
earlier which uses request->ioprio and the struct request seems to be  
the logical place to keep the ioprio. So, please don't cleanup the  
ioprio from there.

Thanks,
Divyesh

>
> - Fernando
>



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