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Date: Tue, 15 Jan 2002 21:35:10 +0100 (CET)
From: Ingo Molnar <mingo@elte.hu>
Reply-To: <mingo@elte.hu>
To: Davide Libenzi <davidel@xmailserver.org>
Cc: Linus Torvalds <torvalds@transmeta.com>,
        lkml <linux-kernel@vger.kernel.org>
Subject: [patch] O(1) scheduler, -I1
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On Tue, 15 Jan 2002, Davide Libenzi wrote:

> >  - RT scheduling is broken.
>
> Why ?

RR tasks were queued to the expired array.

> [...] Ingo, IMHO is not correct to give time slices depending on
> priority and we should return to the old TS(nice) behavior.

i agree - but your new patch is broken still, you have the timeslice range
inverted(!) :-)

but never mind, i've fixed this and added the code to -I1, check it out
at:

    http://redhat.com/~mingo/O(1)-scheduler/sched-O1-2.5.2-final-I1.patch

(for the record, i've tested -I1 on SMP and UP as well.)

-I1 also includes a fix from Dave Jones: mmu_context.h was still included
in arch/i386/kernel/process.c.

> [...] IMVHO is not correct to have new tasks to fully inherit parent
> priority because :

i fully agree - in -I0 i have kept the 'child gets 10% less priority than
parent' rule. This works really well in fork-bomb situations, i've tested
this with -I0. (and -I1 as well.) It also works well with interactive
shells, which want to start processes which will inherit *some* of their
parent's priority, but not all of it.

> 2) if an interactive task is born we do not need an immediate priority
> boost

Think about starting a simple 'ls' under X if under some high load. This
works just fine under 2.5.2-vanilla and 2.5.2-I0 as well. We should give
the task a chance to finish within ... 500 or 1000 msecs (or so), most
shell commands that fork do so.

> 3) if a cpu bound task born from an interactive task ( very very common )
> 	it'll make a long run on the cpu before falling in the hell of cpu
> 	bound tasks
>
> I've also decreased the minimum time slice to 10ms and increased the
> max to 160ms and this should cast back niced tasks to low cpu usages.

(i've done this already in -I0, based on earlier comments of yours.)

> I'm using it in my desk and just to have fun i keep running make -j20
> in background:-)

please re-test this with -I1. (i've tested it and it works just fine, but
more testing cannot hurt.)

are there any other items in your patch that are not yet in -I1?

	Ingo

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