COE 186 Flashcards
Is the maximum time within which it must complete its execution
Deadline
A real-time task is said to be _____ if producing the result after its deadline may cause catastrophic consequences on the system under control.
hard
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.
firm
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.
soft
A real-time operating system that is able to handle hard real-time tasks
hard real-time system
Very important basic properties that real-time systems must have to support critical applications.
- Timeliness
- Predictability
- Efficiency
- Robustness
- Fault tolerance
- Maintainability
Is a technique used by many peripheral devices to transfer data between the device and the main memory
Direct memory access (DMA)
Is a fast memory that is inserted as a buffer between the CPU and the random-access memory (RAM) to speed up processes’ execution.
Cache
It occurs when a high-priority task is blocked by a low-priority task for an unbounded interval of time
Priority inversion
is a computation that is executed by the CPU in a sequential fashion
process
The operation of suspending the running task and inserting it into the ready queue
preemption
A __________ is an assignment of tasks to the processor, so that each task is executed until completion.
Schedule
A schedule is said to be _________ if all tasks can be completed according to a set of specified constraints.
feasible
A set of tasks is said to be _________ if there exists at least one algorithm that can produce a feasible schedule
schedulable
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
Arrival time aᵢ
is the time necessary to the processor for executing the task without interruption
Computation time Cᵢ
is the time before which a task should be completed to avoid damage to the system
Absolute Deadline dᵢ
is the difference between the absolute deadline and the request time
Relative Deadline Dᵢ
is the time at which a task starts its execution
Start time sᵢ
is the time at which a task finishes its execution
Finishing time fᵢ
is the difference between the finishing time and the request time
Response time Rᵢ
is a parameter related to the consequences of missing the deadline (typically, it can be hard, firm, or soft).
Criticality
represents the relative importance of the task with respect to the other tasks in the system
Value vᵢ
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
Lateness Lᵢ
Relative Deadline formula
Dᵢ = dᵢ - rᵢ
Response time formula
Rᵢ = fᵢ - rᵢ
Lateness formula
Lᵢ = fᵢ - dᵢ
is the time a task stays active after its deadline
Tardiness or Exceeding time Eᵢ
is the maximum time a task can be delayed on its activation to complete within its deadline
Laxity or Slack time Xᵢ
Laxity or Slack time formula
Xᵢ = dᵢ - aᵢ - Cᵢ
consist of an infinite sequence of identical activities, called instances or jobs, which are regularly activated at a constant rate
Periodic tasks
consist of an infinite sequence of identical jobs (or instances); however, their activations are not regularly interleaved
Aperiodic tasks
The activation time of the first periodic instance (τi,1)
phase
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.
Deadlock
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
Earliest deadline first (EDF) algorithm
is the variation of end-to-end transfer delay (i.e., the
difference between the maximum and minimum values of transfer delay)
Jitter of packet (or delay jitter)
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
Hyperperiod
is priority level associated with a semaphore or a resource according to an access protocol.
Ceiling
is a kernel data structure used to synchronize the execution of concur-rent jobs.
Semaphore
