linux-kernel - Re: [PATCH v10 clocksource 1/7] clocksource: Provide module parameters to inject delays in watchdog

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Message-ID: <877dkmmq4q.ffs@nanos.tec.linutronix.de>
Date:   Wed, 28 Apr 2021 16:37:41 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Luming Yu <luming.yu@...il.com>, paulmck@...nel.org
Cc:     Andi Kleen <ak@...ux.intel.com>,
        LKML <linux-kernel@...r.kernel.org>, john.stultz@...aro.org,
        sboyd@...nel.org, corbet@....net, Mark.Rutland@....com,
        maz@...nel.org, kernel-team@...com, neeraju@...eaurora.org,
        feng.tang@...el.com, zhengjun.xing@...el.com,
        Chris Mason <clm@...com>
Subject: Re: [PATCH v10 clocksource 1/7] clocksource: Provide module parameters to inject delays in watchdog

On Wed, Apr 28 2021 at 22:24, Luming Yu wrote:
> On Wed, Apr 28, 2021 at 9:57 PM Paul E. McKenney <paulmck@...nel.org> wrote:
>> Therefore, the code marks the clock unstable if it has four bad reads
>> in a row, as it should.
>
> The hard problem to solve is tsc is still in good shape and it can be verified
> with a quick cross check with other thread/core's tsc counts in the
> injected situation or in real life case
> to prove if it is  truly a tsc problem or reference clock's problem of
> the watchdog.
>
> Ideally, we could factor out hard-to-debug unstable tsc problems from
> clock source watchdog problems
> and get less and less tsc sightings caused by clock source watchdog.

The only way to fix this is at the hardware level. Everything else is
wishful thinking.

Thanks,

        tglx