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

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Date:   Wed, 23 Jun 2021 17:25:08 +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 17:13, Odin Ugedal <odin@...d.al> wrote:
>
> ons. 23. jun. 2021 kl. 15:56 skrev Vincent Guittot <vincent.guittot@...aro.org>:
> >
> >
> > The pelt value of sched_entity is synced with  cfs and its contrib
> > before being removed.
>
>
> Hmm. Not sure what you mean by sched_entity here, since this is only
> taking the "removed" load_avg
> and removing it from cfs_rq, together with (removed.load_avg *
> divider) from load_sum. (Although. ".removed" comes from
> a sched entity)

The sched_entity's load_avg that is put in removed.load, is sync with
the cfs_rq PELT signal, which includes contrib, before being added to
removed.load.

>
> > 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
>
> For what it is worth, I am now able to reproduce it (maybe
> CONFIG_HZ=300/250 is the thing) as reported by Sachin,
> and my patch makes it disappear. Without my patch I see situations
> where _sum is zero while _avg is eg. 1 or 2 or 14 (in that range).

hmm, so there is something wrong in the propagation

> This happens for both load, runnable and util.
>
> Lets see what Sachin reports back.
>
> Thanks
> Odin