On 3 May 2017 at 11:37, Peter Zijlstra <pet...@infradead.org> wrote: > > 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's mainly based on the regression i see on my platform. I haven't find the root cause of the regression but it's there which means that using group_entity's load_avg to propagate child cfs_rq runnable_load_avg breaks something > > > 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. What propose Tejun is to break the group's load_avg and make it follows child cfs_rq's runnable_load_avg instead of child cfs_rq's load_avg so it will be difficult if not possible to try to move load_balance on load_avg and remove runnable_load_avg later on if load_avg doesn't work anymore as expected. So keeping group's load_avg working correctly seems a key point Then, we know that we still have wrong behavior with runnable_load_avg when running task's load are really different. so it fixes part of wider problem IMO > > Of course, we should not regress either, I'll go read up on that part. >
