Real-Time Operating Systems

Scheduling metrics
¿ n tasks
¿ Average response time
t r = Σ i=1…N (f i –a i )/n
¿ Total completion time
t c = max i=1…N (f i ) – max i=1…N (a i )
¿ Weighted sum of completion times
J i
S i
C i
f i
d i
t
a i
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¿ Maximum lateness
t r = Σ i=1…N w i f i
L max = max i=1…N (f i - d i )
¿ Maximum # of late tasks
N late = Σ i=1…N miss i
miss i = 0 if f i £ d i, , 1 otherwise
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Scheduling metrics
¿ Average response time/total completion time not
appropriate for hard real time tasks
¿ Maximum lateness: useful for “exploration”
¿ Max # of late task more significant
¿ Often conflicting:
Minimizing maximum
lateness does not
minimize number
of tasks that miss
their deadlines:
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