Messages in this thread | | | From | Vincent Guittot <> | Date | Thu, 14 Apr 2022 09:37:39 +0200 | Subject | Re: [PATCH 1/1] [PATCH v2]sched/pelt: Refine the enqueue_load_avg calculate method |
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On Thu, 14 Apr 2022 at 03:59, Kuyo Chang <kuyo.chang@mediatek.com> wrote: > > From: kuyo chang <kuyo.chang@mediatek.com> > > I meet the warning message at cfs_rq_is_decayed at below code. > > SCHED_WARN_ON(cfs_rq->avg.load_avg || > cfs_rq->avg.util_avg || > cfs_rq->avg.runnable_avg) > > Following is the calltrace. > > Call trace: > __update_blocked_fair > update_blocked_averages > newidle_balance > pick_next_task_fair > __schedule > schedule > pipe_read > vfs_read > ksys_read > > After code analyzing and some debug messages, I found it exits a corner > case at attach_entity_load_avg which will cause load_sum is null but > load_avg is not. > Consider se_weight is 88761 according by sched_prio_to_weight table. > And assume the get_pelt_divider() is 47742, se->avg.load_avg is 1. > By the calculating for se->avg.load_sum as following will become zero > as following. > se->avg.load_sum = > div_u64(se->avg.load_avg * se->avg.load_sum, se_weight(se)); > se->avg.load_sum = 1*47742/88761 = 0. > > After enqueue_load_avg code as below. > cfs_rq->avg.load_avg += se->avg.load_avg; > cfs_rq->avg.load_sum += se_weight(se) * se->avg.load_sum; > > Then the load_sum for cfs_rq will be 1 while the load_sum for cfs_rq is 0. > So it will hit the warning message. > > In order to fix the corner case, make sure the se->load_avg|sum is correct > before enqueue_load_avg. > > After long time testing, the kernel warning was gone and the system runs > as well as before.
This needs a fix tag: Fixes: f207934fb79d ("sched/fair: Align PELT windows between cfs_rq and its se")
> > Signed-off-by: kuyo chang <kuyo.chang@mediatek.com>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
> --- > > v1->v2: > > (1)Thanks for suggestion from Peter Zijlstra & Vincent Guittot. > (2)By suggestion from Vincent Guittot, > rework the se->load_sum calculation method for fix the corner case, > make sure the se->load_avg|sum is correct before enqueue_load_avg. > (3)Rework changlog. > > kernel/sched/fair.c | 8 +++++--- > 1 file changed, 5 insertions(+), 3 deletions(-) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index d4bd299d67ab..159274482c4e 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -3829,10 +3829,12 @@ static void attach_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *s > > se->avg.runnable_sum = se->avg.runnable_avg * divider; > > - se->avg.load_sum = divider; > - if (se_weight(se)) { > + se->avg.load_sum = se->avg.load_avg * divider; > + if (se_weight(se) < se->avg.load_sum) { > se->avg.load_sum = > - div_u64(se->avg.load_avg * se->avg.load_sum, se_weight(se)); > + div_u64(se->avg.load_sum, se_weight(se)); > + } else { > + se->avg.load_sum = 1; > } > > enqueue_load_avg(cfs_rq, se); > -- > 2.18.0 >
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