From m2 -------- Original message -------- Sender: John Locke <jlockefree@xxxxxxxxx> Time: Thu 1/21 17:53 To: kernelnewbies@xxxxxxxxxxxxxxxxx Subject: CFS: Scheduler: How does each change in 'nice' value result in 10% change in CPU time? >Can anyone explain how the weights that the 'nice' values are mapped >to actually result in an ~10% change in CPU time as you go from one >nice level to the next? I can't make out how the comment here actually >computes: (https://git.kernel.org/cgit/linux/kernel/git/stable/linux-stable.git/tree/kernel/sched/sched.h?id=refs/tags/v3.10.94#n918) > >/* > * Nice levels are multiplicative, with a gentle 10% change for every > * nice level changed. I.e. when a CPU-bound task goes from nice 0 to > * nice 1, it will get ~10% less CPU time than another CPU-bound task > * that remained on nice 0. > * > * The "10% effect" is relative and cumulative: from _any_ nice level, > * if you go up 1 level, it's -10% CPU usage, if you go down 1 level > * it's +10% CPU usage. (to achieve that we use a multiplier of 1.25. > * If a task goes up by ~10% and another task goes down by ~10% then > * the relative distance between them is ~25%.) > */ >static const int prio_to_weight[40] = { > >If I take an example of 2 tasks both with weight=1024 (NICE_0) they >should each get 50% of the CPU time. If 1 of the tasks is reniced to >NICE_1 then the NICE_0 task will get 1024/(1024+820)=56% of the CPU >time and the NICE_1 task will get 44% of the CPU time. I'm obviously >not understanding something since I can't come at those 10% figures in >the comments. > >Thanks. > >_______________________________________________ >Kernelnewbies mailing list >Kernelnewbies@xxxxxxxxxxxxxxxxx >http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
_______________________________________________ Kernelnewbies mailing list Kernelnewbies@xxxxxxxxxxxxxxxxx http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
