Re: [RFC][PATCH 18/22] sched: add reclaiming logic to -deadline tasks

[Luca Abeni]

On 12/11/10 17:04, Peter Zijlstra wrote:
> On Fri, 2010-11-12 at 16:36 +0100, Raistlin wrote:
> > But at this point I can't avoid asking. That model aims at _pure_
> > hard real-time scheduling *without* resource reservation capabilities,
> > provided it deals with temporal overruns by means of a probabilistic
> > analysis, right?
>
> > From what I understood from it, its a soft real-time scheduling
> algorithm with resource reservation. It explicitly allows for deadline
> misses, but requires the tardiness of those misses to be bounded, ie.
> the UNC soft real-time definition.
>
> The problem the stochastic execution time model tries to address is the
> WCET computation mess, WCET computation is hard and often overly
> pessimistic, resulting in under-utilized systems.
[...]
BTW, sorry for the shameless plug, but even with the current 
SCHED_DEADLINE you are not forced to dimension the runtime using the 
WCET. You can use some stochastic analysis, providing probabilistic 
deadline guarantees. See (for example) "QoS Guarantee Using 
Probabilistic Deadlines"
http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.22.7683&rep=rep1&type=pdf
and "Stochastic analysis of a reservation based system"
http://www.computer.org/portal/web/csdl/doi?doc=doi/10.1109/IPDPS.2001.925049
(sorry, this is not easy to download... But I can provide a copy if you 
are interested).


			Luca
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