![]() Smaller targets yield better interactivity and a closer approximation to perfect multitasking. This target is called the targeted latency. ![]() To calculate the actual timeslice, CFS sets a target for its approximation of the "infinitely small" scheduling duration in perfect multitasking.CFS uses the nice value to weight the proportion of processor a process is to receive.So, to make similar to perfect multitasking, each process receive 1/n of the processor's time, where n is the number of runnable processes. But in our real world, processor only can run one process at a moment. This model is called perfect multitasking. In an ideal, perfectly multitasking processor, we would run both processes simultaneously, each at 50% power. The nice value acts as a weight, changing the proportion of the processor time each process receives.ĬFS is based on a simple concept : model process scheduling as if the system had an ideal, perfectly multitasking processor. Processor-bound processes crave long timeslices (to keep their cache hot).ĬFS scheduler assigns processes a proportion of the processor, therefore, the amount of processor time (timeslice) that a process receives is a function of the load of the system. I/O-bound processes do not need longer timeslices (although they do like to run often). ![]() Too short a timeslice causes significant amounts of processor time to be wasted on the overhead of switching processes. Too long a timeslice causes the system to have poor interactive performance. The timeslice (quantum) is the numeric value that represents how long a task can run until it is preempted. See detail explain about priority property rt_priority indicate real-time priority(0-99) which higher number is higher priority. In prio property(0-139), nice value is saved with real-time priority, but in this case, smaller number indicate higher priority. In task_struct, there is no nice property alone. All real-time processes are at a higher priority than normal processes. Higher real-time priority values correspond to a greater priority. Real-time priority : default range from 0 to 99. In Linux, it is a control over the proportion of timeslice. #KERNEL RETRIEVE TIMESLICE USED MAC OS#In Mac OS X, the nice value is a control over the absolute timeslice allotted to a process. Nice values are the standard priority range used in all Unix systems. Larger nice values correspond to a lower priority - being "nice" to the other processes on the system. Nice value : a number from -20 to +19 with a default of 0.
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