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SubjectRe: [RFC][PATCH 09/22] sched: add period support for -deadline tasks
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On Fri, 2010-11-12 at 14:33 +0100, Raistlin wrote:
> On Thu, 2010-11-11 at 20:43 +0100, Peter Zijlstra wrote:
> > > Since you spotted it... The biggest issue here is admission control
> > > test. Right now this is done against task's bandwidth, i.e.,
> > > sum_i(runtime_i/period_i)<=threshold, but it is unfortunately wrong...
> > > Or at least very, very loose, to the point of being almost useless! :-(
> >
> > Right, I have some recollection on that.
> >
> :-)
>
> > So sufficient (but not necessary) means its still a pessimistic approach
> > but better than the one currently employed, or does it mean its
> > optimistic and allows for unschedulable sets to be allowed in?
> >
> Tommaso already gave the best possible explanation of this! :-P
>
> So, trying to recap:
> - using runtime/min(deadline,period) _does_ guarantee schedulability,
> but also rejects schedulable situations in UP/partitioning. Quite
> sure it _does_not_ guarantee schedulability in SMP/global, but
> *should* enable bounded tardiness;
> - using runtime/period _does_not_ guarantee schedulability nor in
> UP/partitioning neither in SMP/global, but *should* enable bounded
> tardiness for _both_.

> Thus, all this being said, what do you want me to do? :-D

runtime/min(deadline,period) sounds fine, as its more useful than
runtime/period.


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