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Operating Systems: Virtualization, Concurrency & Persistence

Weighting (Niceness)

Explore how the niceness level adjusts a process's priority in the Completely Fair Scheduler. Learn to calculate process weights and time slices, and understand how these affect CPU allocation and virtual runtime dynamics.

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Nice level of a process

CFS also enables controls over process priority, enabling users or administrators to give some processes a higher share of the CPU. It does this not ...

C
static const int prio_to_weight[40] = {
    /* -20 */ 88761, 71755, 56483, 46273, 36291, 
    /* -15 */ 29154, 23254, 18705, 14949, 11916, 
    /* -10 */ 9548, 7620, 6100, 4904, 3906, 
    /* -5 */ 3121, 2501, 1991, 1586, 1277, 
    /* 0 */ 1024, 820, 655, 526, 423, 
    /* 5*/ 335, 272, 215, 172, 137, 
    /* 10 */ 110, 87, 70, 56, 45, 
    /*15*/ 36, 29, 23, 18, 15,
};

These weights allow us to compute the effective time slice of each process (as we did before), but now accounting for their priority differences. The formula used to do so is as follows:

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