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From:   Thomas Gleixner <tglx@linutronix.de>
To:     Vladimir Oltean <olteanv@gmail.com>
Cc:     Kurt Kanzenbach <kurt.kanzenbach@linutronix.de>,
        Alison Wang <alison.wang@nxp.com>, catalin.marinas@arm.com,
        will@kernel.org, paulmck@kernel.org, mw@semihalf.com,
        leoyang.li@nxp.com, vladimir.oltean@nxp.com,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        Anna-Maria Gleixner <anna-maria@linutronix.de>,
        Peter Zijlstra <peterz@infradead.org>
Subject: Re: [RFC PATCH] arm64: defconfig: Disable fine-grained task level IRQ time accounting
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References: <20200729033934.22349-1-alison.wang@nxp.com> <877dumbtoi.fsf@kurt> <20200729094943.lsmhsqlnl7rlnl6f@skbuf> <87mu3ho48v.fsf@kurt> <20200730082228.r24zgdeiofvwxijm@skbuf> <873654m9zi.fsf@kurt> <87lfiwm2bj.fsf@nanos.tec.linutronix.de> <20200803114112.mrcuupz4ir5uqlp6@skbuf>
Date:   Mon, 03 Aug 2020 17:13:18 +0200
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Vladimir Oltean <olteanv@gmail.com> writes:
>>  1) When irq accounting is disabled, RT throttling kicks in as
>>     expected.
>> 
>>  2) With irq accounting the RT throttler does not kick in and the RCU
>>     stall/lockups happen.
>> 
>> Not much, but there is clearly interaction between irq time accounting
>> and scheduler accounting.
>> 
>> Can you please reduce /proc/sys/kernel/sched_rt_runtime_us in steps of
>> 50000? At least in theory, reduction should bring the throttling back.
>
> We already know from my original report that reducing
> sched_rt_runtime_us to 80% (800000) gives us a stable system.
> https://lkml.org/lkml/2020/6/4/1062

Oh. Somehow missed that. Btw, can you please use links in the form of:

    https://lore.kernel.org/r/$MSGID

lkml.org is spotty and having the message id allows to search in the
mail client as well.

> What is this telling us?

It seems that the fine grained irq time accounting affects the runtime
accounting in some way which I haven't figured out yet.

Thanks,

        tglx