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Chapter 10 : Case Study - UNIX - page 19 / 48

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Ceng 334 - Operating Systems

10-19

UNIX Scheduler (2)

Once a second the priority of all processes are recalculated to avoid starvation using

priority = CPU_usage + nice + base

CPU_usage, represents the average number of clock ticks per second that the process has had during the past few seconds

Nice is a value between –20 to 20 (default 0). Nice system call can be used to set this value 0-20

Base is a system parameter in UNIX source code

The scheduler forces CPU bound (on positive queues) get any service that is left over when all I/O bound and interactive processes are blocked

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