Re: IO Priorities

[Jens Axboe <axboe@suse.de>]

On Mon, Dec 13 2004, Jeff Sipek wrote:
> On Mon, Dec 13, 2004 at 03:38:10PM +0100, Jens Axboe wrote:
> > On Mon, Dec 13 2004, Jeff Sipek wrote:
> > > Hello all,
> > > 	About a week ago, I said I would try to implement IO priorities.
> > > I tried. I got the whole thing done, but there is one major problem - it
> > 
> > I did too, did you see my patch?
> 
> I did after I sent mine. I was reading it and I noticed:
> 
> "Disable TCQ in the hardware/driver by default. Can be changed (as
> always) with the max_depth setting. If you do that, don't expect
> fairness or priorities to work as well."
> 
> Would this cause my problem?

Only if you test on SCSI with TCQ enabled. But I already outlined what
your problems are even if you did.

> > Additionally, you don't do anything with the priorities internally.
> 
> Sure I do, I multiply the slice by cfq_prio_scale[ioprio]. It did seem
> too simple. :-) Looking at your code right now, I kind of see some code
> that should have been in my implementation as well. Back to coding...
> :-)

If you would base changes on what I already did with CFQ, that would be
handy. You need the CFQ bits anyways.

Updated patch here:

http://www.kernel.org/pub/linux/kernel/people/axboe/patches/v2.6/2.6.10-rc3-mm1/cfq-time-slices-11-2.6.10-rc3-mm1.gz

-- 
Jens Axboe