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35. Process Priorities and Scheduling > Process Priorities (Nice Values)

Process Priorities (Nice Values)

On Linux, as with most other UNIX implementations, the default model for scheduling processes for use of the CPU is round-robin time-sharing. Under this model, each process in turn is permitted to use the CPU for a brief period of time, known as a time slice or quantum. Round-robin time-sharing satisfies two important requirements of an interactive multitasking system:

  • Fairness: Each process gets a share of the CPU.

  • Responsiveness: A process doesn’t need to wait for long periods before it receives use of the CPU.

Under the round-robin time-sharing algorithm, processes can’t exercise direct control over when and for how long they will be able to use the CPU. By default, each process in turn receives use of the CPU until its time slice runs out or it voluntarily gives up the CPU (for example, by putting itself to sleep or performing a disk read). If all processes attempt to use the CPU as much as possible (i.e., no process ever sleeps or blocks on an I/O operation), then they will receive a roughly equal share of the CPU.


  

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