Every preemption of one task by another task potentially results in two context

Question

Every preemption of one task by another task potentially results in two context switch activities: one switch from the lower-priority task and one switch back again when the preempting task completes. This means that each time a higher-priority task ?h preempts a lower-priority task ?l , the scheduler must perform the following actions:

-Save context of ?l

-Load context of ?h

-Let ?h execute until completion

-Save context of ?h for the next instance

-Load context of ?l

Assume that for all the tasks, the time to save the context is at most Csave and the time to load the context is Cload . Extend the original response time analysis formula for rate monotonic scheduling to consider context switches among tasks. Even for a task that is never preempted, its execution time must be added by Csave and Cload .

Explanation / Answer

Solution:

Suppose there are x processes with the preemption and z processes without the preemption.

and number of context switches between the preempted processes is y

then

the rate will be= x*y(Csave+Cload) + z*(Csave+Cload)

This will be the time for completion of all the processes.

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