linux-kernel - Re: [RESEND][RFC] BFQ I/O Scheduler

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Message-ID: <20080415091139.GC29846@gandalf.sssup.it>
Date:	Tue, 15 Apr 2008 11:11:39 +0200
From:	Fabio Checconi <fchecconi@...il.com>
To:	Jens Axboe <jens.axboe@...cle.com>
Cc:	linux-kernel@...r.kernel.org, paolo.valente@...more.it
Subject: Re: [RESEND][RFC] BFQ I/O Scheduler

> From: Jens Axboe <jens.axboe@...cle.com>
> Date: Tue, Apr 15, 2008 10:22:36AM +0200
>
> On Tue, Apr 01 2008, Fabio Checconi wrote:
...
> > We would greatly appreciate any sort of feedback from you, comments,
> > suggestions, corrections and so on.  Thank you for your attention.
> 
> Fabio, I've merged the scheduler for some testing. Overall the code
> looks great, you've done a good job!
> 

thank you very much :)

> I didn't touch patches 2 and 3, but I rewrote #1 somewhat. See the
> result here:
> 
> http://git.kernel.dk/?p=linux-2.6-block.git;a=commitdiff;h=973a02c4ea1c324c41e45b69c074b13d3bfa97de;hp=a985aabe4d7a720b109c2b63549f8641676a9c88
> 
> I'm sure you'll agree with the hlist_sched_*() functions. I also killed
> the ->bfq_ioprio_changed modification, what exactly was the purpose of
> that?
> 

of course the hlist_sched_*() functions are much better than what was
in the patch (the idea behind the patch was to not touch at all cfq code).

the ->bfq_ioprio_changed was there to avoid that a process/ioc doing
i/o on multiple devices managed by cfq and bfq would see ioprio
changes only for one of the two schedulers.

cfq_ioc_set_ioprio() (and its bfq counterpart bfq_ioc_set_ioprio())
unconditionally assign 0 to (bfq_)ioprio_changed, so the first
scheduler that sees the ioprio change eats the new priority values.
of course I may be wrong, but I think it (or some better mechanism
to avoid the problem) is necessary.

> The code is now in the 'bfq' branch of the block git repo.
> 

of course we'll be glad to help in testing in any way you can find useful.

thank you!
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