On Tue, Aug 23, 2016 at 04:39:51PM +0100, Dietmar Eggemann wrote: > On 23/08/16 15:45, Vincent Guittot wrote: > > On 23 August 2016 at 16:13, Peter Zijlstra <pet...@infradead.org> wrote: > >> On Tue, Aug 23, 2016 at 03:28:19PM +0200, Vincent Guittot wrote: > >>> I still wonder if using a flat util hierarchy is the right solution to > >>> solve this problem with utilization and task group. I have noticed > >>> exact same issues with load that generates weird task placement > >>> decision and i think that we should probably try to solve both wrong > >>> behavior with same mechanism. but this is not possible with flat > >>> hierarchy for load > >>> > >>> Let me take an example. > >>> TA is a always running task on CPU1 in group /root/level1/ > >>> TB wakes up on CPU0 and moves TA into group /root/level2/ > >>> Even if TA stays on CPU1, runnable_load_avg of CPU1 root cfs rq will > >>> become 0. > >> > >> Because while we migrate the load_avg on /root/level2, we do not > >> propagate the load_avg up the hierarchy? > > > > yes. At now, the load of a cfs_rq and the load of its sched_entity > > that represents it at parent level are disconnected > > I guess you say 'disconnected' because cfs_rq and se (w/ cfs_rq eq. > se->my_q) are now independent pelt signals where as before the rewrite > they were 'connected' for load via __update_tg_runnable_avg(), > __update_group_entity_contrib() in __update_entity_load_avg_contrib() > and for utilization via 'se->avg.utilization_avg_contrib = > group_cfs_rq(se)->utilization_load_avg' in > __update_entity_utilization_avg_contrib(). I don't understand what exactly "disconnected" means, but with respect to group_entity's load_avg, nothing is changed essentially:
group_entity_load_avg = my_cfs_rq_load_avg / tg_load_avg * tg_shares