COE 186

Question 1

Is the maximum time within which it must complete its execution

Answer 1

Deadline

Question 2

A real-time task is said to be _____ if producing the result after its deadline may cause catastrophic consequences on the system under control.

Answer 2

hard

Question 3

Areal-time task is said to be ______ if producing the results after its deadline is useless for the system, but does not cause any damage.

Answer 3

firm

Question 4

A real-time task is said to be _____ if producing the results after its deadline has still some utility for the system, although causing a performance degradation.

Answer 4

soft

Question 5

A real-time operating system that is able to handle hard real-time tasks

Answer 5

hard real-time system

Question 6

Very important basic properties that real-time systems must have to support critical applications.

Answer 6

• Timeliness
• Predictability
• Efficiency
• Robustness
• Fault tolerance
• Maintainability

Question 7

Is a technique used by many peripheral devices to transfer data between the device and the main memory

Answer 7

Direct memory access (DMA)

Question 8

Is a fast memory that is inserted as a buffer between the CPU and the random-access memory (RAM) to speed up processes’ execution.

Answer 8

Cache

Question 9

It occurs when a high-priority task is blocked by a low-priority task for an unbounded interval of time

Answer 9

Priority inversion

Question 10

is a computation that is executed by the CPU in a sequential fashion

Answer 10

process

Question 11

The operation of suspending the running task and inserting it into the ready queue

Answer 11

preemption

Question 12

A __________ is an assignment of tasks to the processor, so that each task is executed until completion.

Answer 12

Schedule

Question 13

A schedule is said to be _________ if all tasks can be completed according to a set of specified constraints.

Answer 13

feasible

Question 14

A set of tasks is said to be _________ if there exists at least one algorithm that can produce a feasible schedule

Answer 14

schedulable

Question 15

is the time at which a task becomes ready for execution; it is also referred to as request time or release time and indicated by rᵢ

Answer 15

Arrival time aᵢ

Question 16

is the time necessary to the processor for executing the task without interruption

Answer 16

Computation time Cᵢ

Question 17

is the time before which a task should be completed to avoid damage to the system

Answer 17

Absolute Deadline dᵢ

Question 18

is the difference between the absolute deadline and the request time

Answer 18

Relative Deadline Dᵢ

Question 19

is the time at which a task starts its execution

Answer 19

Start time sᵢ

Question 20

is the time at which a task finishes its execution

Answer 20

Finishing time fᵢ

Question 21

is the difference between the finishing time and the request time

Answer 21

Response time Rᵢ

Question 22

is a parameter related to the consequences of missing the deadline (typically, it can be hard, firm, or soft).

Answer 22

Criticality

Question 23

represents the relative importance of the task with respect to the other tasks in the system

Answer 23

Value vᵢ

Question 24

represents the delay of a task completion with respect to its deadline; note that if a task completes before the deadline, its lateness is negative

Answer 24

Lateness Lᵢ

Question 25

Relative Deadline formula

Answer 25

*Dᵢ = dᵢ - rᵢ*

Question 26

Response time formula

Answer 26

*Rᵢ = fᵢ - rᵢ*

Question 27

Lateness formula

Answer 27

*Lᵢ = fᵢ - dᵢ*

Question 28

is the time a task stays active after its deadline

Answer 28

Tardiness or Exceeding time *Eᵢ*

Question 29

is the maximum time a task can be delayed on its activation to complete within its deadline

Answer 29

Laxity or Slack time *Xᵢ*

Question 30

Laxity or Slack time formula

Answer 30

*Xᵢ = dᵢ - aᵢ - Cᵢ*

Question 31

consist of an infinite sequence of identical activities, called instances or jobs, which are regularly activated at a constant rate

Answer 31

Periodic tasks

Question 32

consist of an infinite sequence of identical jobs (or instances); however, their activations are not regularly interleaved

Answer 32

Aperiodic tasks

Question 33

The activation time of the first periodic instance (τi,1)

Answer 33

phase

Question 34

is a situation in which two or more tasks are blocked indefinitely because each task is waiting for a resource acquired by another blocked task.

Answer 34

Deadlock

Question 35

is a scheduling algorithm which assigns dynamic priorities to tasks according to their absolute deadlines: the task with the shortest deadline is assigned the highest priority

Answer 35

Earliest deadline first (EDF) algorithm

Question 36

is the variation of end-to-end transfer delay (i.e., the difference between the maximum and minimum values of transfer delay)

Answer 36

Jitter of packet (or delay jitter)

Question 37

it is the minimum interval of time after which the schedule repeats itself. If H is the length of such an interval, then the schedule in [0,H) is the same as that in [kH, (k + 1)H], for any integer k > 0

Answer 37

Hyperperiod

Question 38

is priority level associated with a semaphore or a resource according to an access protocol.

Answer 38

Ceiling

Question 39

is a kernel data structure used to synchronize the execution of concur-rent jobs.

Answer 39

Semaphore