Messages in this thread | | | Subject | Re: [PATCH v3] sched: fix first task of a task group is attached twice | From | Dietmar Eggemann <> | Date | Wed, 1 Jun 2016 16:31:09 +0100 |
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On 30/05/16 16:52, Vincent Guittot wrote: > The cfs_rq->avg.last_update_time is initialize to 0 with the main effect > that the 1st sched_entity that will be attached, will keep its
attached in .task_move_group ?
I'm not sure if we can have a .switched_to() directly followed by a .enqueue_task() into a cfs_rq with avg.last_update_time = 0.
> last_update_time set to 0 and will attached once again during the > enqueue. > Initialize cfs_rq->avg.last_update_time to 1 instead.
Maybe worth mentioning in the header:
This double se attaching for the first task which moves into the task group owning this cfs_rq (.task_move_group() and .enqueue_task()) can (obviously) only happen if CONFIG_FAIR_GROUP_SCHED is set.
The reason for this is that we set 'se->avg.last_update_time = cfs_rq->avg.last_update_time' in attach_entity_load_avg() and use 'migrated = !sa->last_update_time' as a flag in enqueue_entity_load_avg() to decide if we call attach_entity_load_avg() (again) or only update se->avg .
Tested-by: Dietmar Eggemann <Dietmar.Eggemann@arm.com>
> Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org> > --- > > v3: > - add initialization of load_last_update_time_copy for not 64bits system > - move init into init_cfs_rq > > v2: > - rq_clock_task(rq_of(cfs_rq)) can't be used because lock is not held > > kernel/sched/fair.c | 10 ++++++++++ > 1 file changed, 10 insertions(+) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index 218f8e8..86be9c1 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -8459,6 +8459,16 @@ void init_cfs_rq(struct cfs_rq *cfs_rq) > cfs_rq->min_vruntime_copy = cfs_rq->min_vruntime; > #endif > #ifdef CONFIG_SMP > + /* > + * Set last_update_time to something different from 0 to make > + * sure the 1st sched_entity will not be attached twice: once > + * when attaching the task to the group and one more time when > + * enqueueing the task. > + */ > + cfs_rq->avg.last_update_time = 1; > +#ifndef CONFIG_64BIT > + cfs_rq->load_last_update_time_copy = 1; > +#endif > atomic_long_set(&cfs_rq->removed_load_avg, 0); > atomic_long_set(&cfs_rq->removed_util_avg, 0); > #endif
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