Re: [RFC][PATCH 09/22] sched: add period support for -deadlinetasks

[Raistlin]

On Thu, 2010-11-11 at 20:17 +0100, Peter Zijlstra wrote:
> On Fri, 2010-10-29 at 08:34 +0200, Raistlin wrote:
> > Make it possible to specify a period (different or equal than
> > deadline) for -deadline tasks.
> > 
> I would expect it to be:
> 
> runtime <= deadline <= period
> 
Well, apart from that really unhappy comment/changelog, it should be
like that in the code, and if it's not, it is what I meant and I'll
change to that as soon as I can! :-)

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! :-(

The more correct --in the sense that it at least yield a sufficient (not
necessary!) condition-- thing to do would be
sum_i(runtime_i/min{deadline_i,period_i})<=threshold.

So, what you think we should do? Can I go for this latter option?

Thanks,
Dario

-- 
<<This happens because I choose it to happen!>> (Raistlin Majere)
----------------------------------------------------------------------
Dario Faggioli, ReTiS Lab, Scuola Superiore Sant'Anna, Pisa  (Italy)

http://blog.linux.it/raistlin / raistlin@xxxxxxxxx /
dario.faggioli@xxxxxxxxxx

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