The scheduling algorithm in regards to the nice value of a process

The kernel does timeslicing of it’s cpu resource. Each process is given a certain slice. Yet the size of this size is determined by the priority (nice value). The priority is handled dynamically. So when a process hasn’t had enough cpu time, it’ll receive a higher priority. This also works the other way around, a process that had been running for a long time, will receive a low priority (cfr with a higher nice value).

The ‘Starvation’ protection

“In Linux, process priority is dynamic. The scheduler keeps track of what processes are doing and adjusts their priorities periodically; in this way, processes that have been denied the use of the CPU for a long time interval are boosted by dynamically increasing their priority. Correspondingly, processes running for a long time are penalized by decreasing their priority.”

Het scheduling concept

“Linux scheduling is based on the time-sharing technique already introduced in the section “CPU’s Time Sharing” in Chapter 5, Timing Measurements: several processes are allowed to run “concurrently,” which means that the CPU time is roughly divided into “slices,” one for each runnable process.[1] Of course, a single processor can run only one process at any given instant. If a currently running process is not terminated when its time slice or quantum expires, a process switch may take place. ”

“The Linux scheduling algorithm works by dividing the CPU time into epochs. In a single epoch, every process has a specified time quantum whose duration is computed when the epoch begins. In general, different processes have different time quantum durations. The time quantum value is the maximum CPU time portion assigned to the process in that epoch.”

“Each process has a base time quantum: it is the time-quantum value assigned by the scheduler to the process if it has exhausted its quantum in the previous epoch. The users can change the base time quantum of their processes by using the nice( ) and setpriority( ) system calls.”

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