Re: [PATCH] sched/fair: vruntime should normalize when switching from fair

[Steve Muckle <smuckle@google.com>]

On 09/27/2018 05:43 PM, Wanpeng Li wrote:
>>> On your CPU4:
>>> scheduler_ipi()
>>>    -> sched_ttwu_pending()
>>>         -> ttwu_do_activate()    => p->sched_remote_wakeup should be
>>> false, so ENQUEUE_WAKEUP is set, ENQUEUE_MIGRATED is not
>>>              -> ttwu_activate()
>>>                   -> activate_task()
>>>                        -> enqueue_task()
>>>                             -> enqueue_task_fair()
>>>                                  -> enqueue_entity()
>>>                                       bool renorm = !(flags &
>>> ENQUEUE_WAKEUP) || (flags & ENQUEUE_MIGRATE)
>>> so renorm is false in enqueue_entity(), why you mentioned that the
>>> cfs_rq->min_vruntime is still added to the se->vruntime in
>>> enqueue_task_fair()?
>>
>> Maybe this is a misunderstanding on my side but didn't you asked me to
>> '... Could you point out when the fair rq's min_vruntime is added to the
>> task's vruntime in your *later* scenario? ...'
> 
> Yeah, if the calltrace above and my analysis is correct, then the fair
> rq's min_vruntime will not be added to the task's vruntime in your
> *later* scenario, which means that your patch is not necessary.

In the scenario I observed, the task is not waking - it is running and 
being deboosted from priority inheritance, transitioning from RT to CFS.

Dietmar and I both were able to reproduce the issue with the testcase I 
posted earlier in this thread.

thanks,
Steve