Re: request->ioprio

[Rusty Russell <rusty@rustcorp.com.au>]

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.