On 20 May 2016 at 12:12, Morten Rasmussen <[email protected]> wrote: > On Fri, May 13, 2016 at 09:23:50AM +0200, Vincent Guittot wrote: >> On 12 May 2016 at 21:42, Yuyang Du <[email protected]> wrote: >> > On Thu, May 12, 2016 at 03:31:27AM -0700, tip-bot for Peter Zijlstra wrote: >> >> Commit-ID: 1be0eb2a97d756fb7dd8c9baf372d81fa9699c09 >> >> Gitweb: >> >> http://git.kernel.org/tip/1be0eb2a97d756fb7dd8c9baf372d81fa9699c09 >> >> Author: Peter Zijlstra <[email protected]> >> >> AuthorDate: Fri, 6 May 2016 12:21:23 +0200 >> >> Committer: Ingo Molnar <[email protected]> >> >> CommitDate: Thu, 12 May 2016 09:55:33 +0200 >> >> >> >> sched/fair: Clean up scale confusion >> >> >> >> Wanpeng noted that the scale_load_down() in calculate_imbalance() was >> >> weird. I agree, it should be SCHED_CAPACITY_SCALE, since we're going >> >> to compare against busiest->group_capacity, which is in [capacity] >> >> units. >> >> In fact, load_above_capacity is only about load and not about capacity. >> >> load_above_capacity -= busiest->group_capacity is an optimization (may >> be a wronf one) of >> load_above_capacity -= busiest->group_capacity * SCHED_LOAD_SCALE / >> SCHED_CAPACITY_SCALE >> >> so we subtract load to load > > I like your approach as you compute the desired minimum load, which is > essentially finding the number of NICE_0_LOAD task we want in the group, > and then determine how much excess load there is. So it becomes quite > clear that it is load. > > While it preserves existing behaviour I would question the whole > NICE_0_LOAD assumption. It totally falls apart with PELT and if we have > tasks with nice != 0.
yes, i haven't found a simple use case yet to demonstrate the usefulness of this part > > Also, it doesn't address the existing unit issue as load_above_capacity > is later multiplied by busiest->group_capacity when computing the > imbalance. As said in the other thread, we should either kill the > minimum load estimation that assumes always-running NICE_0_LOAD tasks, > or at least make sure the scaling of load_above_capacity is correct. > Patches attempting either solution are in the other thread.
