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

From: Luca Abeni
Date: Fri Nov 12 2010 - 12:45:38 EST


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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