Scheduling Flashcards
What is long term scheduling?
decides when a process should enter the ready state to start competing for cpu
what is short term scheduling?
decides which of the ready processes should run next on the cpu
what is “real time in system” in terms of short term scheduling?
the total time since a process has entered the ready list
which form of scheduling to arrival and departure times play a role?
long term
what is a batch process?
performs longish running repetitive tasks without human intervention, like payroll processing on a certain day of the month
what is average turnaround time?
average over a set of processes arrival and departure times
in a very large process queue, Round Robin scheduling can look like __________
FIFO
what is multilevel scheduling?
when there are separate queues that hold PRIORITY…the higher queues execute with higher priority. inside of each queue round robin is used
what is a real time process?
a process that is characterized by continual input. something like video or audio and the computer MUST respond to and handle this
what is rate monotonic algorithm?
schedules processes according to “period” which is to say, the process with the highest frequency of running gets prioritized highest (is preemptive)
what is earliest deadline first algorithm?
schedules task according to the deadline of the task. the closer the deadline the higher priority (is preemptive)
what is the difference between asymmetric multiprocessing and symmetric multiprocessing?
in asymmetric, 1 CPU handles all the scheduling, I/O and other things while the other CPUs execute only user code. but in a symmetric setup, they all split the load equally
what is memory stall?
the time a CPU takes waiting for memory/data to become available
how do multithreaded cores solve memory stall?
while one thread is waiting for memory, the other can continue processing
what is push and pull migration?
a form of load balancing. push means that a task checks the processor load and redistributes to other CPUs…whereas pull means a CPU core may go get tasks to process if it’s queue is empty
what is processor affinity?
when a process relies on cache on a specific CPU and thus due to the cost of invalidating the cache generally stays running on the same CPU
what is the difference between coarse-grained and fine-grained hardware multithreading?
course-grained: threads execute until a long-latency event occurs like memory lookup
fine grained: fine-grained makes the switch much more regularly
what is the difference between hard and soft affinity?
hard affinity means that the OS guarantees that the process will not change CPUs…soft affinity makes no guarantees
what is the difference between hard and soft real time systems?
soft provides no guarantee for critical real time processes whereas hard does
what is admission-control?
the scheduler may not even allow a process to start if it cannot guranatee that it will be completed by it’s deadline
In Little’s formula, λ, represents the ____.
average arrival rate for new processes in the queue
