Task Scheduling Questions and Answers

Answer: C

Correct answer: increasing the priority of the medium priority tasks

Raising the medium tasks makes matters worse: they preempt the low priority task holding the lock and lengthen the time the high priority task waits, which is unbounded priority inversion in its classic form. The other three all shorten or eliminate the blocking.

Answer: D

Running at the elevated priority is exactly what prevents an intermediate task from extending the wait, so the blocking reduces to the length of the critical section. The mechanism named in the second statement is the reason for the property claimed in the first.

Answer: A

The minimum interarrival time is what makes the load boundable and therefore analysable; an aperiodic task may in principle arrive at any rate and cannot be guaranteed. Most real event handling is sporadic once the physics is examined.

Answer: B

Correct answer: bound the interference aperiodic work can cause the periodic tasks

Aperiodic work has no period, so it cannot be included in a schedulability analysis as it stands. A sporadic server gives it a budget and a replenishment rule, so it behaves like a periodic task from the analysis’s point of view and its worst-case interference is known in advance.

Answer: C

Correct answer: run without being preempted by tasks below a stated priority

A task runs at its normal priority when ready but, once running, cannot be preempted by anything below its threshold. This reduces the number of preemptions and lets tasks share stack space, at the cost of some responsiveness - a useful trade where memory is the binding constraint.

Answer: D

Two switches per release, one in and one out, are charged to the task being released, which keeps the analysis in its usual form. On a set with short periods and a slow switch the correction can be several per cent of the processor.

Answer: A

Two hundred cycles per millisecond is two hundred thousand cycles a second out of forty-eight million, a little over four parts in a thousand. Ten such tasks would cost four per cent, which is when the correction starts to matter.

Answer: B

Rate monotonic loses its optimality as soon as deadlines and periods part company, and ordering by relative deadline restores it. The distinction matters for a task sampled every ten milliseconds that must respond within two.

Answer: C

The task remains the lowest priority since its period is still the longest, and its own demand has halved, so nothing above it is affected and it has more time in which to run. Lengthening a period is always safe under rate monotonic; shortening one is not.

Answer: D

Correct answer: possibly unschedulable, the interference on everything below having doubled

Halving the period doubles both that task’s utilisation and the number of times it preempts everything below it in the analysis window. The task itself is unaffected, being highest priority, but every other task now suffers twice the interference from it, and the set must be reanalysed.