Summary ch6

1. Aim of scheduling: Assign processes to be executed by the processor(s)

   -Response time

   -Throughput

   -Processor efficiency

2. Schduling Criteria:

   User-oriented:

   -Response Time: Elapsed time between the submission of a request until there is an output

   -Turnaround Time: The time between the submission and the completion of a process

   System-oriented:

   -Effective and efficient utilization of the processor

3. Two modes：

   Nonpreemptive(非先发制人的)：Once a process is in the running state, it will continue until it terminates or blocks itself for I/O

   Preemptive(先发制人的):

   -Currently running process may be interrupted and moved to the Ready state by the operating system

   -Allows for better service since any one process cannot monopolize the processor for very long

4. First-Come-First-Served

   Disadvantage: A short process may have to wait a very long time before it can execute

   Favors CPU-bound processes

   -I/O processes have to wait until CPU-bound process completes

   -Low utilization for I/O devices

   -Possibly low utilization for processor

5. Round Robin

   -Clock interrupt is generated at periodic intervals

   -When an interrupt occurs, the currently running process is placed in the ready queue,next ready process is selected

   -Known as time slicing

   Favors CPU-bound processes

   -CPU-bound process gets more CPU time

   -I/O process has to wait for CPU-bound processes to consume their quanta before its turn of executing on the CPU

6. Time quantum:

   -The time interval between two clock interrupts

   -The maximum time allocated to a process’s execution in each turn

7. Shortest Process Next

   -Process with shortest expected processing time is selected next

   -Short process jumps ahead of longer processes

   -Nonpreemptive policy

8. Shortest Remaining Time

   Preemptive version of shortest process next policy

9. Highest Response Ratio Next