Messages in this thread | | | Subject | Re: [PATCH] sched/fair: vruntime should normalize when switching from fair | From | Dietmar Eggemann <> | Date | Wed, 29 Aug 2018 16:33:32 +0100 |
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On 08/29/2018 12:59 PM, Peter Zijlstra wrote: > On Wed, Aug 29, 2018 at 11:54:58AM +0100, Dietmar Eggemann wrote: >> I forgot to mention that since fair_task's cpu affinity is restricted to >> CPU4, there is no call to set_task_cpu()->migrate_task_rq_fair() since if >> (task_cpu(p) != cpu) fails. >> >> I think the combination of cpu affinity of the fair_task to CPU4 and the >> fact that the scheduler runs on CPU1 when waking fair_task (with the two >> cpus not sharing LLC) while TTWU_QUEUE is enabled is the situation in which >> this vruntime issue can happen. > > Ohhh, D'0h. A remote wakeup that doesn't migrate.
Ah, there is this WF_MIGRATED flag, perfect for the distinction whether a task migrated or not.
> That would suggest something like so: > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index b39fb596f6c1..b3b62cf37fb6 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -9638,7 +9638,8 @@ static inline bool vruntime_normalized(struct task_struct *p) > * - A task which has been woken up by try_to_wake_up() and > * waiting for actually being woken up by sched_ttwu_pending(). > */ > - if (!se->sum_exec_runtime || p->state == TASK_WAKING) > + if (!se->sum_exec_runtime || > + (p->state == TASK_WAKING && p->sched_remote_wakeup)) > return true; > > return false; Yes, this solves the issue for the case I described. Using 'p->sched_remote_wakeup' (WF_MIGRATED) looks more elegant than using 'p->sched_class == &fair_sched_class'.
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