Re: [RFC] Scheduler issue 1, RT tasks ...

Davide Libenzi
2001-12-29T22:23:04Z

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On Sat, 29 Dec 2001, Dieter [iso-8859-15] Nützel wrote:

> Martin Knoblauch wrote:
> >
> > > Re: [RFC] Scheduler issue 1, RT tasks ...
> > >
> > > >
> > > > Right, that was my question. George says, in your words, "for better
> > >
> > > > standards compliancy ..." and I want to know why you guys think
> > > that.
> > >
> > > The thought was that if someone need RT tasks he probably need a very
> > > low latency and so the idea that by applying global preemption decisions
> > > would lead to a better compliancy. But i'll be happy to ear that this is
> > > false anyway ...
> > >
> >
> > without wanting to start a RT flame-fest, what do people really want
> > when they talk about RT in this [Linux] context:
> >
> > - very low latency
> > - deterministic latency ("never to exceed")
> > - both
> > - something completely different
> >
> > All of the above from time to time and user to user. That is, some
> > folks want one or more of the above, some folks want more, some less.
> > What is really up? Well they have a job to do that requires certain
> > things. Different jobs require different capabilities. It is hard to
> > say that any given system will do a reasonably complex job with out
> > testing. For example we may have the required latency but find the
> > system fails because, to get the latency, we preempted another task that
> > was (and so still is) in the middle of updating something we need to
> > complete the job.
>
> So George what direction should I try for some tests?
> 2.4.17 plus your and Robert's preempt plus lock-break?
> Add your high-res-timers, rtscheduler or both?
> Do they apply against 2.4.17/2.4.18-pre1?
> A combination of the above plus Davide's BMQS?
>
> I ask because my MP3/Ogg-Vorbis hiccup during dbench isn't solved anyway.
> Running 2.4.17 + preempt + lock-break + 10_vm-21 (AA).
> Some wisdom?

A bad scheduler can make the latency to increase but in your case i don't
think that it could increase that much ( in percent ). By copying a huge
file arund you can experience spots of 1-2 secs of machine freeze and
this is definitely not the scheduler. The demage the a bad scheduler can
do is directly proportional to the cs anyway.

- Davide