linux-kernel - Re: [RFC PATCH] arm64: defconfig: Disable fine-grained task level IRQ time accounting

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Message-ID: <20200730082228.r24zgdeiofvwxijm@skbuf>
Date:   Thu, 30 Jul 2020 11:22:28 +0300
From:   Vladimir Oltean <olteanv@...il.com>
To:     Kurt Kanzenbach <kurt.kanzenbach@...utronix.de>
Cc:     Alison Wang <alison.wang@....com>, catalin.marinas@....com,
        will@...nel.org, paulmck@...nel.org, mw@...ihalf.com,
        leoyang.li@....com, vladimir.oltean@....com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Anna-Maria Gleixner <anna-maria@...utronix.de>
Subject: Re: [RFC PATCH] arm64: defconfig: Disable fine-grained task level
 IRQ time accounting

On Thu, Jul 30, 2020 at 09:23:44AM +0200, Kurt Kanzenbach wrote:
> Hi Vladimir,
> 
> On Wed Jul 29 2020, Vladimir Oltean wrote:
> > For more context, here is my original report of the issue:
> > https://lkml.org/lkml/2020/6/4/1062
> >
> > Just like you, I could not reproduce the RCU stalls and system hang on a
> > 5.6-rt kernel, just on mainline and derivatives, using the plain
> > defconfig.
> >
> > The issue is not specific to Layerscape or i.MX8, but rather I was able
> > to see the same behavior on Marvell Armada 37xx as well as Qualcomm
> > MSM8976.
> >
> > So, while of course I agree that disabling IRQ time accounting for arm64
> > isn't a real solution, it isn't by far an exaggerated proposal either.
> > Nonetheless, the patch is just a RFC and should be treated as such. We
> > are at a loss when it comes to debugging this any further and we would
> > appreciate some pointers.
> 
> Yeah, sure. I'll try to reproduce this issue first. So it triggers with:
> 
>  * arm64
>  * mainline, not -rt kernel
>  * opened serial console
>  * irq accounting enabled
> 
> Anything else?
> 
> Thanks,
> Kurt

Thanks for giving a helping hand, Kurt. The defconfig should be enough.
In the interest of full disclosure, the only arm64 device on which we
didn't reproduce this was the 16-core LX2160A. But we did reproduce on
that with maxcpus=1 though. And also on msm8976 with all 8 cores booted.
Just mentioning this in case you're testing on a 16-core system, you
might want to reduce the number a bit.

Thanks,
-Vladimir