Processor Management Flashcards
What is processor scheduling
Processor scheduling refers to how we allocate CPU cores to processes. In other words, how to manage transitions of processes between the ready and running states to ensure efficient resource utilization.
What are the top 4 most common scheduling algorithms (1 processor)
1 first come first served
2 round robin
3 shortest process next
4 multilevel queuing
What is the first come first served scheduling algorithm
Allocates the processor based on the creation time of processes.
What are the pros of the first come first served scheduling algorithm
- There is no unnecessary switching between processes
- You will eventually always provide processing time to a given process
What are the cons of the first come first served scheduling algorithm
The average waiting time (the total time spent in the ready state) is often long
What is the round-robin scheduling algorithm
Identical to first come first served, except that no process can occupy the processor longer than a predefined time length (the time quantum).
What are the pros of the round robin scheduling algorithm
Distributes resources in a “fair” manner
A quick process can pass through relatively quickly
What are the cons of the round robin scheduling algorithm
Long average waiting time when processes require multiple time quanta
Performance depends heavily on time quantum
What is the shortest process next scheduling algorithm
The shortest process next scheduling algorithm shares the processor on the basis of shortest predicted execution time.
What can the shortest process next algorithm be
Preemptive (processes may be interrupted before they are done)
Non-preemptive (processes may not be interrupted before they are done)
What are the pros of the shortest process Next
Gives the minimum average waiting time for a given set of processes
What are the cons of the shortest process next
Execution time has to be estimated
Longer processes may have to wait a very long time
What are the 3 design choices for Multilevel Queuing
Design choices:
(a) How map processes to queues?
(b) How determine relative priority of queues?
(c) Which scheduling algorithm to use within each queue?
What are the different specific queues for multilevel queueing
interactive processes (processes with lots of I/O)
normal processes (e.g., system services)
batch processes (processes without I/O)
What are the two relative priority queues
- Fixed priority scheduling
- Time slicing
What is fixed priority scheduling
Example: interactive processes always get priority over batch processes.
What is time-slicing in Multilevel queueing
Allocates CPU time based on a specific percentage to different types of processes.
Example: 80% of the CPU time to in- teractive processes, 10% to normal pro- cesses, 10% to batch processes.
In a round robin scheduling algorithm what will happen after the process arrives at the processor
1) be interrupted and placed at the back of the (circular) queue, or 2) complete before it runs out of time.
What are the pros of multilevel queueing
Complex, can accommodate a range of different performance objectives
What are the cons of multilevel queueing
Complex and difficult to calibrate.
What are user oriented scheduling criteria
- Turnaround time
- Response time
What are system oriented scheduling criteria/measurement
- Throughput
- Processor utilization
Define turnaround time
The time between the submission of a process and its completion
Define response time
The time between the submission of a process and its first response
