Re: [PATCH] V-3.0 Single Priority Array O(1) CPU Scheduler Evaluation

William Lee Irwin III
2004-08-04T01:51:22Z

>> Aperiodic rotations defer movement until MAX_RT_PRIO's slot is evacuated.

On Wed, Aug 04, 2004 at 11:36:59AM +1000, Peter Williams wrote:
> Unfortunately, to ensure no starvation, promotion has to continue even
> when there are tasks in MAX_RT_PRIO's slot.

One may either demote to evict MAX_RT_PRIO immediately prior to
rotation or rely on timeslice expiry to evict MAX_RT_PRIO. Forcibly
evicting MAX_RT_PRIO undesirably accumulates tasks at the fencepost.

William Lee Irwin III wrote:
>> The primary concern was that ticklessness etc. may require it to occur
>> during context switches.

On Wed, Aug 04, 2004 at 11:36:59AM +1000, Peter Williams wrote:
> On a tickless system, I'd consider using a timer to control when
> do_promotions() gets called. I imagine something similar will be
> necessary to manage time slices?

This is an alternative to scheduler accounting in context switches.
Periodicity often loses power conservation benefits.

-- wli