Re: scheduler interactivity: timeslice calculation seem wrong

[Nick Piggin]

Eric St-Laurent wrote:

> currently, nicer tasks (nice value toward -20) get larger timeslices,
> and less nice tasks (nice value toward 19) get small timeslices.

Funny, isn't it!

> this is contrary to all process scheduling theory i've read, and also
> contrary to my intuition.

Yep.

> maybe it was done this way for fairness reasons, but that's another
> story...
>
> high priority (interactive) tasks should get small timeslices for best
> interactive feeling, and low priority (cpu hog) tasks should get large
> timeslices for best efficiency, anyway they can be preempted by higher
> priority tasks if needed.

Its done this way because this is really how the priorities are
enforced. With some complicated exceptions, every task will be
allowed to complete 1 timeslice before any task completes 2
(assuming they don't block).

So higher priority tasks need bigger timeslices.

> also, i think dynamic priority should be used for timeslice calculation
> instead of static priority. the reason is, if a low priority task get a
> priority boost (to prevent starvation, for example) it should use the
> small timeslice corresponding to it's new priority level, instead of
> using it's original large timeslice that can ruin the interactive feel.

Among other things, yes, I think this is a good idea too. I'll be
addressing both these issues in my scheduler fork.

I do have dynamic timeslices, but currently high priority tasks
still get big timeslices.


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