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SubjectRe: a different approach to scheduling issues
On Thu, 1 Oct 1998, Jeremy Fitzhardinge wrote:

> On 01-Oct-98 Rik van Riel wrote:
> > The main problem is that the scheduling code is very
> > time critical.
>
> Actually, scheduling isn't especially time-critical, but context
> switching is.

OK.

> It's quite common for systems to only recalculate priorities every
> second or so, even if they're switching contexts much more rapidly.
> This allows you to do more interesting/complex scheduling decisions
> without everything bogging down. Maybe you could even run the
> scheduler in user-mode as an RT task...

Hmm. Although it is an interesting idea, it kinda conflicts
with the next part of your message...

> Every now and then (a tunable which depends on how responsive you
> need your dynamic priorities to be) you go through and recalculate
> the relative importance of your running processes.

This is in my patch. It recalculates the importance of
only the running processes as soon as each process on
the runqueue has used up it's timeslice.

> RT processes, of course, never have their priorities changed, so the
> scheduler is essentially a no-op. Sleeping processes never need
> their priorities adjusted until they actually become runnable.

Hey, I did that first! :-) This is in my patch
as well...

Rik.
+-------------------------------------------------------------------+
| Linux memory management tour guide. H.H.vanRiel@phys.uu.nl |
| Scouting Vries cubscout leader. http://www.phys.uu.nl/~riel/ |
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