Messages in this thread | | | Subject | Re: [v4.8-rc1 Regression] sched/fair: Apply more PELT fixes | From | Joseph Salisbury <> | Date | Wed, 19 Oct 2016 10:49:56 -0400 |
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On 10/18/2016 07:56 AM, Vincent Guittot wrote: > Le Tuesday 18 Oct 2016 à 12:34:12 (+0200), Peter Zijlstra a écrit : >> On Tue, Oct 18, 2016 at 11:45:48AM +0200, Vincent Guittot wrote: >>> On 18 October 2016 at 11:07, Peter Zijlstra <peterz@infradead.org> wrote: >>>> So aside from funny BIOSes, this should also show up when creating >>>> cgroups when you have offlined a few CPUs, which is far more common I'd >>>> think. >>> The problem is also that the load of the tg->se[cpu] that represents >>> the tg->cfs_rq[cpu] is initialized to 1024 in: >>> alloc_fair_sched_group >>> for_each_possible_cpu(i) { >>> init_entity_runnable_average(se); >>> sa->load_avg = scale_load_down(se->load.weight); >>> >>> Initializing sa->load_avg to 1024 for a newly created task makes >>> sense as we don't know yet what will be its real load but i'm not sure >>> that we have to do the same for se that represents a task group. This >>> load should be initialized to 0 and it will increase when task will be >>> moved/attached into task group >> Yes, I think that makes sense, not sure how horrible that is with the > That should not be that bad because this initial value is only useful for > the few dozens of ms that follow the creation of the task group > >> current state of things, but after your propagate patch, that >> reinstates the interactivity hack that should work for sure. > The patch below fixes the issue on my platform: > > Dietmar, Omer can you confirm that this fix the problem of your platform too ? > > --- > kernel/sched/fair.c | 9 ++++++++- > 1 file changed, 8 insertions(+), 1 deletion(-)Vinc > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index 8b03fb5..89776ac 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -690,7 +690,14 @@ void init_entity_runnable_average(struct sched_entity *se) > * will definitely be update (after enqueue). > */ > sa->period_contrib = 1023; > - sa->load_avg = scale_load_down(se->load.weight); > + /* > + * Tasks are intialized with full load to be seen as heavy task until > + * they get a chance to stabilize to their real load level. > + * group entity are intialized with null load to reflect the fact that > + * nothing has been attached yet to the task group. > + */ > + if (entity_is_task(se)) > + sa->load_avg = scale_load_down(se->load.weight); > sa->load_sum = sa->load_avg * LOAD_AVG_MAX; > /* > * At this point, util_avg won't be used in select_task_rq_fair anyway > > > > Omer also reports that this patch fixes the bug for him as well. Thanks for the great work, Vincent!
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