On Thu, 27 Sep 2018 at 21:23, Dietmar Eggemann <dietmar.eggem...@arm.com> wrote: > > On 09/27/2018 03:19 AM, Wanpeng Li wrote: > > On Thu, 27 Sep 2018 at 06:38, Dietmar Eggemann <dietmar.eggem...@arm.com> > > wrote: > >> > >> Hi, > >> > >> On 09/26/2018 11:50 AM, Wanpeng Li wrote: > >>> Hi Dietmar, > >>> On Tue, 28 Aug 2018 at 22:55, Dietmar Eggemann <dietmar.eggem...@arm.com> > >>> wrote: > >>>> > >>>> On 08/27/2018 12:14 PM, Peter Zijlstra wrote: > >>>>> On Fri, Aug 24, 2018 at 02:24:48PM -0700, Steve Muckle wrote: > >>>>>> On 08/24/2018 02:47 AM, Peter Zijlstra wrote: > >>>>>>>>> On 08/17/2018 11:27 AM, Steve Muckle wrote: > >> > >> [...] > >> > >>>>>>>>>> - later, when the prio is deboosted and the task is moved back > >>>>>>>>>> to the fair class, the fair rq's min_vruntime is added to > >>>>>>>>>> the task's vruntime, even though it wasn't subtracted > >>>>>>>>>> earlier. > >>> > >>> Could you point out when the fair rq's min_vruntime is added to the > >>> task's vruntime in your *later* scenario? attach_task_cfs_rq will not > >>> do that the same reason as detach_task_cfs_rq. fair task's > >>> sched_remote_wakeup is false which results in vruntime will not be > >>> renormalized in enqueue_entity. > >> > >> The cfs_rq->min_vruntime is still added to the se->vruntime in > >> enqueue_task_fair(). > > > > I understand what your patch done, > > It's not my patch ;-) I just helped to find out under which > circumstances this issue can happen. > > > 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. Regards, Wanpeng Li
