linux-kernel - Re: [PATCH] Give kjournald a IOPRIO_CLASS

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Message-ID: <20081002063606.512decb3@infradead.org>
Date:	Thu, 2 Oct 2008 06:36:06 -0700
From:	Arjan van de Ven <arjan@...radead.org>
To:	Jens Axboe <jens.axboe@...cle.com>
Cc:	Dave Chinner <david@...morbit.com>,
	Andi Kleen <andi@...stfloor.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, Alan Cox <alan@...rguk.ukuu.org.uk>
Subject: Re: [PATCH] Give kjournald a IOPRIO_CLASS_RT io priority

On Thu, 2 Oct 2008 15:27:47 +0200
Jens Axboe <jens.axboe@...cle.com> wrote:

> On Thu, Oct 02 2008, Arjan van de Ven wrote:
> > On Thu, 2 Oct 2008 11:45:37 +0200
> > Jens Axboe <jens.axboe@...cle.com> wrote:
> > 
> > > 
> > > That's a good idea, just bump the priority a little bit. Arjan,
> > > did you test that out? I'd suggest just trying prio level 0 and
> > > still using best-effort scheduling. Probably still need the sync
> > > marking, would be interesting to experiment with though.
> > 
> > I looked at 0 but it appears the 0 is the default for everyone...
> > if everyone just defaulted to > 0 then yes I would have picked 0.
> 
> That's not correct, class BE and value 4 is the default (and the code
> defaults to that, if you haven't set a value yourself):
> 
> #define IOPRIO_NORM     (4)
> static inline int task_ioprio(struct io_context *ioc)
> {
>         if (ioprio_valid(ioc->ioprio))
>                 return IOPRIO_PRIO_DATA(ioc->ioprio);
> 
>         return IOPRIO_NORM;
> }
> 
> static inline int task_ioprio_class(struct io_context *ioc)
> {
>         if (ioprio_valid(ioc->ioprio))
>                 return IOPRIO_PRIO_CLASS(ioc->ioprio);
> 
>         return IOPRIO_CLASS_BE;
> }
> 
> So if you use IOPRIO_CLASS_BE and 0 for the ioprio, you will have the
> highest priority of the default scheduling class.

ok

I checked not by looking at the code, but running ionice -p <pid> on a
bunch of things and they came back as 0 

> 


-- 
Arjan van de Ven 	Intel Open Source Technology Centre
For development, discussion and tips for power savings, 
visit http://www.lesswatts.org
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