linux-kernel - Re: x86-tip tsc/tick gripage

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Message-ID: <20170426102617.l62cdn4gs4h5i4fw@hirez.programming.kicks-ass.net>
Date:   Wed, 26 Apr 2017 12:26:17 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Mike Galbraith <efault@....de>
Cc:     Ingo Molnar <mingo@...nel.org>,
        "Paul E. McKenney" <paulmck@...ibm.com>,
        LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
        Thomas Gleixner <tglx@...utronix.de>,
        Frederic Weisbecker <fweisbec@...il.com>
Subject: Re: x86-tip tsc/tick gripage

On Wed, Apr 26, 2017 at 10:57:42AM +0200, Mike Galbraith wrote:

> Both still lose their TSC.
> 
> [   11.982468] tsc: Refined TSC clocksource calibration: 2260.999 MHz
> [   11.994275] clocksource: tsc: mask: 0xffffffffffffffff max_cycles: 0x20974a4d8bb, max_idle_ns: 440795246623 ns
> [   13.064172] clocksource: Switched to clocksource tsc
> [  240.247851] clocksource: timekeeping watchdog on CPU23: Marking clocksource 'tsc' as unstable because the skew is too large:
> [  240.462501] clocksource:                       'tsc' cs_now: 108fe5be09f cs_last: b90a6a0676 mask: ffffffffffffffff
> [  240.675057] tsc: Marking TSC unstable due to clocksource watchdog


And they didn't use to? We don't typically write to TSC or TSC_ADJUST
and thus would not cause such behaviour.