On 19 October 2016 at 16:49, Joseph Salisbury
<joseph.salisb...@canonical.com> wrote:
> 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 <pet...@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!
Thanks
>
