Re: [RFC 2/5] sched: Add CPU rate soft caps

[Peter Williams <pwil3058@bigpond.net.au>]

Peter Williams wrote:
> Balbir Singh wrote:
> > On 5/26/06, Peter Williams <pwil3058@bigpond.net.au> wrote:
> > <snip>
> > > Notes:
> > >
> > > 1. To minimize the overhead incurred when testing to skip caps 
> > > processing for
> > > uncapped tasks a new flag PF_HAS_CAP has been added to flags.
> > >
> > > 2. The implementation involves the addition of two priority slots to the
> > > run queue priority arrays and this means that MAX_PRIO no longer
> > > represents the scheduling priority of the idle process and can't be 
> > > used to
> > > test whether priority values are in the valid range.  To alleviate this
> > > problem a new function sched_idle_prio() has been provided.
> >
> > I am a little confused by this. Why link the bandwidth expired tasks a
> > cpu (its caps) to a priority slot? Is this a hack to conitnue using
> > the prio_array? why not move such tasks to the expired array?
>
> Because it won't work as after the array switch they may get to run 
> before tasks who aren't exceeding their cap (or don't have a cap).

Another important reason for using these slots is that it allows waking 
tasks to preempt tasks that have exceeded their cap.

Peter
--
Peter Williams                                   pwil3058@bigpond.net.au

"Learning, n. The kind of ignorance distinguishing the studious."
 -- Ambrose Bierce
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