Analysis: CPU Load Analysis
CPU Load Analysis
For D < T , the biggest period during which the CPU is permanently used (i.e. without interruption, idle time) corresponds to the scenario in which all tasks are activated synchronously. This period is called synchronous busy period and has duration L.
L can be computed by the following iterative method, which returns the first instant since the synchronous activation in which the CPU completes all the submitted jobs.
Knowing L, we have to guarantee the Load Condition , i.e.
The Load Condition refers to all the work that must be completed by t.
How to compute h(t)?
Example:
Task set Γ = {(2, 4), (2, 8), (3, 16)}.
Draw the Gantt chart and mark the points where tasks must complete.
Write a suitable equation.
Knowing L we have to guarantee the load condition, i.e.
And h(t) can be computed as follows:
The computation of h(t) for all values of t ∈ [0, L[ is unfeasible.
However it is enough computing the load condition for the instants in which the load function varies, i.e.
Note: there are other, possibly shorter, values for L.
EDF Scheduling
-> Schedulability not guaranteed.
But the CPU load analysis indicates that the task set is schedulable!
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