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SubjectRe: 2.6.0-test2-mm1 results
> On Fri, 1 Aug 2003 01:19, Martin J. Bligh wrote:
>> >> Does this help interactivity a lot, or was it just an experiment?
>> >> Perhaps it could be less agressive or something?
>> >
>> > Well basically this is a side effect of selecting out the correct cpu
>> > hogs in the interactivity estimator. It seems to be working ;-) The more
>> > cpu hogs they are the lower dynamic priority (higher number) they get,
>> > and the more likely they are to be removed from the active array if they
>> > use up their full timeslice. The scheduler in it's current form costs
>> > more to resurrect things from the expired array and restart them, and the
>> > cpu hogs will have to wait till other less cpu hogging tasks run.
>> >
>> > How do we get around this? I'll be brave here and say I'm not sure we
>> > need to, as cpu hogs have a knack of slowing things down for everyone,
>> > and it is best not just for interactivity for this to happen, but for
>> > fairness.
>> >
>> > I suspect a lot of people will have something to say on this one...
>> Well, what you want to do is prioritise interactive tasks over cpu hogs.
>> What *seems* to be happening is you're just switching between cpu hogs
>> more ... that doesn't help anyone really. I don't have an easy answer
>> for how to fix that, but it doesn't seem desireable to me - we need some
>> better way of working out what's interactive, and what's not.
> Indeed and now that I've thought about it some more, there are 2 other
> possible contributors
> 1. Tasks also round robin at 25ms. Ingo said he's not sure if that's too low,
> and it definitely drops throughput measurably but slightly.
> A simple experiment is changing the timeslice granularity in sched.c and see
> if that fixes it to see if that's the cause.
> 2. Tasks waiting for 1 second are considered starved, so cpu hogs running with
> their full timeslice used up when something is waiting that long will be
> expired. That used to be 10 seconds.
> Changing starvation limit will show if that contributes.

Ah. If I'm doing a full "make -j" I have almost 100 tasks per cpu.
if it's 25ms or 100ms timeslice that's 2.5 or 10s to complete the
timeslice. Won't that make *everyone* seem starved? Not sure that's
a good idea ... reminds me of Dilbert: "we're going to focus particularly
on ... everything!" ;-)


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