On Wed, May 03, 2017 at 09:34:51AM +0200, Vincent Guittot wrote: > We use load_avg for calculating a stable share and we want to use it > more and more. So breaking it because it's easier doesn't seems to be > the right way to do IMHO
So afaict we calculate group se->load.weight (aka shares, see calc_cfs_shares), using cfs_rq->avg.load_avg, which feeds into tg->load_avg through cfs_rq->tg_load_avg_contrib and cfs_rq->load.weight. And cfs_rq->avg.load_avg is computed from cfs_rq->load.weight, which is \Sum se->load.weight. OTOH group se->avg.load_avg isn't used much, which is TJ's point. The only cases where group se->avg.load_avg are relevant to cfs_rq->avg.load are the cases I listed yesterday, group creation and group destruction. There we use the group se->avg.load_avg to manage the boundary conditions. So with the proposed change to se->avg.load_avg we can have some (temporary) boundary effect when you destroy a lot of (previously active) cgroups. Of course, it could be I overlooked something, in which case, please tell :-) That said, I agree it would be nice to entirely get rid of runnable_avg, but that is a much larger change and would require a lot more work. I don't immediately see why we can't fix the thing now and then work on removing runnable_load_avg later. Of course, we should not regress either, I'll go read up on that part.
