Process and Thread Scheduling
Process and Thread Scheduling
Raju Pandey
Department of Computer Sciences
University of California, Davis
Winter 2005
Scheduling
? Context switching
? an interrupt occurs (device completion, timer interrupt)
? a thread causes a trap or exception
? may need to choose a different thread/process to run
? We glossed over the choice of which process or thread is
chosen to be run next
? ¡°some thread from the ready queue¡±
? This decision is called scheduling
o scheduling is a policy
o context switching is a mechanism
ECS 150A (Operating Systems)
Source: Gribble, Lazowska, Levy,
Zahorjan
Scheduling, 2
Objectives
? After this lecture, you should understand:
? the goals of scheduling.
? preemptive vs. non-preemptive scheduling.
? the role of priorities in scheduling.
? scheduling criteria.
? common scheduling algorithms.
ECS 150A (Operating Systems)
Instructor: Raju Pandey
Scheduling, 3
Basic Concepts
? Maximum CPU
utilization obtained
with
multiprogramming
? CPU¨CI/O Burst
Cycle ¨C Process
execution consists
of a cycle of CPU
execution and I/O
wait
? CPU burst
distribution
ECS 150A (Operating Systems)
Instructor: Raju Pandey
Scheduling, 4
Histogram of CPU-burst Times
Exponential/HyperExponential
I/O bound: Many short cpu bursts
CPU bound: few very long cpu bursts
ECS 150A (Operating Systems)
Instructor: Raju Pandey
Scheduling, 5
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