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

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Date:   Wed, 23 Jun 2021 14:22:18 +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 14:18, Odin Ugedal <odin@...d.al> wrote:
>
> Hi,
>
> Wouldn't the attached diff below also help when load is removed,
> Vincent? Isn't there a theoretical chance that x_sum ends up at zero
> while x_load ends up as a positive value (without this patch)? Can
> post as a separate patch if it works for Sachin.

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

>
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index bfaa6e1f6067..def48bc2e90b 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -3688,15 +3688,15 @@ update_cfs_rq_load_avg(u64 now, struct cfs_rq *cfs_rq)
>
>                 r = removed_load;
>                 sub_positive(&sa->load_avg, r);
> -               sub_positive(&sa->load_sum, r * divider);
> +               sa->load_sum = sa->load_avg * divider;
>
>                 r = removed_util;
>                 sub_positive(&sa->util_avg, r);
> -               sub_positive(&sa->util_sum, r * divider);
> +               sa->util_sum = sa->util_avg * divider;
>
>                 r = removed_runnable;
>                 sub_positive(&sa->runnable_avg, r);
> -               sub_positive(&sa->runnable_sum, r * divider);
> +               sa->runnable_sum = sa->runnable_avg * divider;
>
>                 /*
>                  * removed_runnable is the unweighted version of
> removed_load so we