Posted Jul 21, 2010 22:37 UTC (Wed) by blitzkrieg3
In reply to: Example
Parent article: Adding periods to SCHED_DEADLINE
I think their confusion centers around the implications of allowing separate deadline and period values. If the commenters read Dario's email, then they would have seen his reference to the "sporadic task model" which may have helped.
Yeah exactly. I went back and read the email after seeing the response, and the key point is:
one of the tasks can miss its deadline by 3 time units in the worst case (if, and if yes which one, depends on the order with witch they arrive).
Obviously if we have the good fortune of having P2 arrive after 5 time units, we're golden. Before reading the email, I would have assumed that if you're just starting an executable, rather than acting on an event such as a udp packet or something, then you can sacrifice 5 time units.
I've illustrated exactly what I mean http://imgur.com/CKMcp.png
For the purposes of explaining how this works and what these values mean, it might make more sense to use a simple example that isn't schedule-able, no matter what order it comes in, like:
T_1 = (2, 4, 3)
T_2 = (2, 5, 3)
Even if T_2 can be scheduled after 2 time units, using the naive algorithm that I illustrated in the picture, it's clear that they're both going to wake up at the same time after 10 units, at which time you have 3 units to schedule 4 slots of cpu time.
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