Re: [PATCH v3 4/5] sched: sync a se with its cfs_rq when switching sched class to fair class

Byungchul Park
2015-08-20T05:24:20Z

On Wed, Aug 19, 2015 at 07:12:41PM +0200, Peter Zijlstra wrote:
> On Wed, Aug 19, 2015 at 03:47:15PM +0900, byungchul.park@lge.com wrote:
> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > index 1be042a..3419f6c 100644
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -2711,6 +2711,17 @@ static inline void update_load_avg(struct sched_entity *se, int update_tg)
> >
> > static void attach_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se)
> > {
> > + /*
> > + * in case of migration and cgroup-change, more care should be taken
> > + * because se's cfs_rq was changed, that means calling __update_load_avg
> > + * with new cfs_rq->avg.last_update_time is meaningless. so we skip the
> > + * update here. we have to update it with prev cfs_rq just before changing
> > + * se's cfs_rq, and get here soon.
> > + */
> > + if (se->avg.last_update_time)
> > + __update_load_avg(cfs_rq->avg.last_update_time, cpu_of(rq_of(cfs_rq)),
> > + &se->avg, 0, 0, NULL);
> > +
> > se->avg.last_update_time = cfs_rq->avg.last_update_time;
> > cfs_rq->avg.load_avg += se->avg.load_avg;
> > cfs_rq->avg.load_sum += se->avg.load_sum;
>
> you seem to have forgotten to remove the same logic from
> enqueue_entity_load_avg(), which will now call __update_load_avg()
> twice.

i am sorry for not catching what you want to say. enqueue_entity_load_avg()
calls __update_load_avg() in normal case, that is, not having changed its
cfs_rq, while in case having changed its cfs_rq, we only need to attach the
average load assuming that __update_load_avg() was already called when its
cfs_rq was changed.

is there anything i missed? could you let me know if yes?

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