linux-kernel - Re: [powerpc][next-20210621] WARNING at kernel/sched/fair.c:3277 during boot

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Date:   Wed, 23 Jun 2021 15:55:47 +0200
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     Odin Ugedal <odin@...d.al>
Cc:     Sachin Sant <sachinp@...ux.vnet.ibm.com>,
        Linux Next Mailing List <linux-next@...r.kernel.org>,
        linuxppc-dev@...ts.ozlabs.org,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [powerpc][next-20210621] WARNING at kernel/sched/fair.c:3277
 during boot

On Wed, 23 Jun 2021 at 14:37, Odin Ugedal <odin@...d.al> wrote:
>
> ons. 23. jun. 2021 kl. 14:22 skrev Vincent Guittot <vincent.guittot@...aro.org>:
> >
> > In theory it should not because _sum should be always larger or equal
> > to _avg * divider. Otherwise, it means that we have something wrong
> > somewhere else
>
> Yeah, that might be the case. Still trying to wrap my head around
> this. I might be wrong, but isn't there a possibility
> that avg->period_contrib is increasing in PELTs accumulate_sum,
> without _sum is increasing. This makes the pelt divider increase,
> making the statement "_sum should be always larger or equal to _avg *"
> false? Or am I missing something obvious here?

The pelt value of sched_entity is synced with  cfs and its contrib
before being removed.
Then, we start to remove this load in update_cfs_rq_load_avg() before
calling __update_load_avg_cfs_rq so contrib should not have change and
we should be safe

>
> Still unable to reproduce what Sachin is reporting tho.
>
> Odin