linux-kernel - Re: allow non root users to set io priority "idle" ?

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Message-ID: <f6ca9fed0708071435h31531279gb6ea0fc760be98df@mail.gmail.com>
Date:	Tue, 7 Aug 2007 23:35:27 +0200
From:	dragoran <drago01@...il.com>
To:	"Jens Axboe" <jens.axboe@...cle.com>
Cc:	"Andi Kleen" <andi@...stfloor.org>, linux-kernel@...r.kernel.org
Subject: Re: allow non root users to set io priority "idle" ?

so there is no real reason not to allow it for non root users?
removing the check is easy (3 lines) ....
or are there any other issues/problems?

On 8/7/07, Jens Axboe <jens.axboe@...cle.com> wrote:
> On Mon, Aug 06 2007, Andi Kleen wrote:
> > > couldn't this be fixed by bumping idle tasks to middle while they hold a
> >
> > Usually to high.
> >
> > But it's all complicated and hasn't been done consistently
> > (there are real time mutexes in the -rt kernel for example,
> > but there are lots of other locks and they have higher overhead too)
> > and it's unclear we really want to do all this complexity anyways.
> >
> > Also as I said the problem could then still happen in user space
> > which then would all need to be fixed to handle PI too.
> >
> > In some cases the relationship is also not as simple as a single
> > lock. And for IO handling it would be likely quite hard.
> >
> > I personally always found idle priorities quite dubious because
> > even if they worked reliable for the CPU they will clear your cache/
> > load your memory controller and impact all other programs because
> > of this. And for the disk they will cause additional seeks which are
> > also very costly.
>
> But that is why the idle priority implementation in CFQ adds a grace
> period before idle prio tasks are run. So that concern should not be an
> issue, if so the grace period needs to be enlarged. That at least covers
> the seek side of things. If idle io tasks run, then the IO load on the
> system must be very low to zero. Hence other IO relevant resource
> contention isn't an iissue.
>
> --
> Jens Axboe
>
>
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