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

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Date:	Tue, 13 Mar 2007 07:38:18 +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 07:11, Mike Galbraith wrote:
> On Tue, 2007-03-13 at 05:49 +1100, Con Kolivas wrote:
> > On Tuesday 13 March 2007 01:34, Mike Galbraith wrote:
> > > On Mon, 2007-03-12 at 22:23 +1100, Con Kolivas wrote:
> > > > Mike the cpu is being proportioned out perfectly according to
> > > > fairness as I mentioned in the prior email, yet X is getting the
> > > > lower latency scheduling. I'm not sure within the bounds of fairness
> > > > what more would you have happen to your liking with this test case?
> > >
> > > It has been said that "perfection is the enemy of good".  The two
> > > interactive tasks receiving 40% cpu while two niced background jobs
> > > receive 60% may well be perfect, but it's damn sure not good.
> >
> > Again I think your test is not a valid testcase. Why use two threads for
> > your encoding with one cpu? Is that what other dedicated desktop OSs
> > would do?
>
> The testcase is perfectly valid.  My buddies box has two full cores, so
> we used two encoders such that whatever bandwidth is not being actively
> consumed by more important things gets translated into mp3 encoding.
>
> How would you go about ensuring that there won't be any cycles wasted?
>
> _My_ box has 1 core that if fully utilized translates to 1.2 cores.. or
> whatever, depending on the phase of the moon.  But no matter, logical vs
> physical cpu argument is pure hand-waving.  What really matters here is
> the bottom line: your fair scheduler ignores the very real requirements
> of interactivity.

Definitely not. It does not give unfair cpu towards interactive tasks. That's 
a very different argument.

> > And let's not lose sight of things with this one testcase.
> >
> > RSDL fixes
> > - every starvation case
> > - all fairness isssues
> > - is better 95% of the time on the desktop
>
> I don't know where you got that 95% number from.  For the most part, the
> existing scheduler does well.  If it sucked 95% of the time, it would
> have been shredded a long time ago.

Check the number of feedback reports. I don't feel petty enough to count them 
personally to give you an accuracte percentage.

> > If we fix 95% of the desktop and worsen 5% is that bad given how much
> > else we've gained in the process?
>
> Killing the known corner case starvation scenarios is wonderful, but
> let's not just pretend that interactive tasks don't have any special
> requirements.

Now you're really making a stretch of things. Where on earth did I say that 
interactive tasks don't have special requirements? It's a fundamental feature 
of this scheduler that I go to great pains to get them as low latency as 
possible and their fair share of cpu despite having a completely fair cpu 
distribution.

> 	-Mike

-- 
-ck
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