linux-kernel - Re: [PATCH][RSDL-mm 0/7] RSDL cpu scheduler for 2.6.21-rc3-mm2

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Message-Id: <200703131653.39415.kernel@kolivas.org>
Date:	Tue, 13 Mar 2007 16:53:38 +1100
From:	Con Kolivas <kernel@...ivas.org>
To:	Mike Galbraith <efault@....de>
Cc:	Ingo Molnar <mingo@...e.hu>,
	linux kernel mailing list <linux-kernel@...r.kernel.org>,
	ck list <ck@....kolivas.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH][RSDL-mm 0/7] RSDL cpu scheduler for 2.6.21-rc3-mm2

On Tuesday 13 March 2007 16:10, Mike Galbraith wrote:
> On Tue, 2007-03-13 at 09:51 +1100, Con Kolivas wrote:
> > On 13/03/07, Mike Galbraith <efault@....de> wrote:
> > > As soon as your cpu is fully utilized, fairness looses or interactivity
> > > loses.  Pick one.
> >
> > That's not true unless you refuse to prioritise your tasks
> > accordingly. Let's take this discussion in a different direction. You
> > already nice your lame processes. Why? You already have the concept
> > that you are prioritising things to normal or background tasks. You
> > say so yourself that lame is a background task. Stating the bleedingly
> > obvious, the unix way of prioritising things is via nice. You already
> > do that. So moving on from that...
>
> Sure.  If a user wants to do anything interactive, they can indeed nice
> 19 the rest of their box before they start.
>
> > Your test case you ask "how can I maximise cpu usage". Well you know
> > the answer already. You run two threads. I won't dispute that.
> >
> > The debate seems to be centered on whether two tasks that are niced +5
> > or to a higher value is background. In my opinion, nice 5 is not
> > background, but relatively less cpu. You already are savvy enough to
> > be using two threads and nicing them. All I ask you to do when using
> > RSDL is to change your expectations slightly and your settings from
> > nice 5 to nice 10 or 15 or even 19. Why is that so offensive to you?
>
> It's not "offensive" to me, it is a behavioral regression.  The
> situation as we speak is that you can run cpu intensive tasks while
> watching eye-candy.  With RSDL, you can't, you feel the non-interactive
> load instantly.  Doesn't the fact that you're asking me to lower my
> expectations tell you that I just might have a point?

Yet looking at the mainline scheduler code, nice 5 tasks are also supposed to 
get 75% cpu compared to nice 0 tasks, however I cannot seem to get 75% cpu 
with a fully cpu bound task in the presence of an interactive task. To me 
that means mainline is not living up to my expectations. What you're saying 
is your expectations are based on a false cpu expectation from nice 5. You 
can spin it both ways. It seems to me the only one that lives up to a defined 
expectation is to be fair. Anything else is at best vague, and at worst 
starvation prone.

> > Please don't pick 5.none of the above. Please try to work with me on
> > this.
>
> I'm not trying to be pig-headed.  I'm of the opinion that fairness is
> great... until you strictly enforce it wrt interactive tasks.

How about answering my question then since I offered you numerous combinations 
of ways to tackle the problem? The simplest one doesn't even need code, it 
just needs you to alter the nice value that you're already setting.

-- 
-ck
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