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

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Message-ID: <CAKfTPtBKn27=jryS_sxsVb+0yHDze_PMcLuyFtDkDo0H9Nzqww@mail.gmail.com>
Date:   Wed, 23 Jun 2021 18:55:07 +0200
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     Sachin Sant <sachinp@...ux.vnet.ibm.com>
Cc:     Odin Ugedal <odin@...d.al>,
        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 18:46, Sachin Sant <sachinp@...ux.vnet.ibm.com> wrote:
>
>
> > Ok. This becomes even more weird. Could you share your config file and more details about
> > you setup ?
> >
> > Have you applied the patch below ?
> > https://lore.kernel.org/lkml/20210621174330.11258-1-vincent.guittot@linaro.org/
> >
> > Regarding the load_avg warning, I can see possible problem during attach. Could you add
> > the patch below. The load_avg warning seems to happen during boot and sched_entity
> > creation.
> >
>
> Here is a summary of my testing.
>
> I have a POWER box with PowerVM hypervisor. On this box I have a logical partition(LPAR) or guest
> (allocated with 32 cpus 90G memory) running linux-next.
>
> I started with a clean slate.
> Moved to linux-next 5.13.0-rc7-next-20210622 as base code.
> Applied patch #1 from Vincent which contains changes to dequeue_load_avg()
> Applied patch #2 from Vincent which contains changes to enqueue_load_avg()
> Applied patch #3 from Vincent which contains changes to attach_entity_load_avg()
> Applied patch #4 from https://lore.kernel.org/lkml/20210621174330.11258-1-vincent.guittot@linaro.org/
>
> With these changes applied I was still able to recreate the issue. I could see kernel warning
> during boot.
>
> I then applied patch #5 from Odin which contains changes to update_cfs_rq_load_avg()
>
> With all the 5 patches applied I was able to boot the kernel without any warning messages.
> I also ran scheduler related tests from ltp (./runltp -f sched) . All tests including cfs_bandwidth01
> ran successfully. No kernel warnings were observed.

ok so Odin's patch fixes the problem which highlights that we
overestimate _sum or don't sync _avg and _sum correctly

I'm going to look at this further

>
> Have also attached .config in case it is useful. config has CONFIG_HZ_100=y

Thanks, i will have a look

>
> Thanks
> -Sachin
>