Re: idle priority

Rik van Riel (H.H.vanRiel@phys.uu.nl)
Mon, 10 Aug 1998 22:48:50 +0200 (CEST)


On Mon, 10 Aug 1998, Rik van Riel wrote:
> On Sun, 9 Aug 1998, Solar Designer wrote:
>
> > Can we get something like this into the standard kernel, finally?
> >
> > --- linux-2.0.35/include/linux/sched.h Sat Jul 18 22:54:22 1998
> > +++ linux/include/linux/sched.h Wed Aug 5 06:30:50 1998
> [SNIP]
>
> Your implementation has just one problem: it doesn't do task
> switches of multiple SCHED_IDLE processes, since they all have
> the same priority and they don't change position on the runqueue.
>
> It will need the same place-changing behaviour that SCHED_RR
> tasks get upon entering schedule()...

I hate to follow up to my own mail, but there are some other
ideas that occurred to me:

- we want to change schedule_idle() to immediately replace a
SCHED_IDLE process when something else is runnable
- we want _long_ timeslices to maximize speed and to minimize
impact on cache/memory/etc. (say 1 minute)
- [for 2.3.x] we want a 2-level scheduling mechanism with CTSS-like
timeslice adaptation, a limited number of SCHED_IDLE tasks on the
runqueue and some other advanced features like a (small) secondary
idle task which only gets run when the first one takes a fault, we
will then remove the SCHED_RR feature too.

I have some ideas on how to do this in under 1 kB of code, so
I guess it's best that I volunteer for the job :-)

Don't expect it the first weeks however, since I'm super-busy
with my summer-job and I'm also working (in my rare free time)
on the out-of-memory program killer (so that the system continues
to run and kills the major suspect instead of a random process).

It should be ready in early September however...

Rik.
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