linux-kernel - Re: [clocksource] 8901ecc231: stress-ng.lockbus.ops_per

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Date:   Wed, 4 Aug 2021 21:34:13 -0700
From:   Andi Kleen <ak@...ux.intel.com>
To:     paulmck@...nel.org, Chao Gao <chao.gao@...el.com>
Cc:     Feng Tang <feng.tang@...el.com>,
        kernel test robot <oliver.sang@...el.com>,
        John Stultz <john.stultz@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Stephen Boyd <sboyd@...nel.org>,
        Jonathan Corbet <corbet@....net>,
        Mark Rutland <Mark.Rutland@....com>,
        Marc Zyngier <maz@...nel.org>,
        Xing Zhengjun <zhengjun.xing@...ux.intel.com>,
        Chris Mason <clm@...com>, LKML <linux-kernel@...r.kernel.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        lkp@...ts.01.org, lkp@...el.com, ying.huang@...el.com,
        zhengjun.xing@...el.com
Subject: Re: [clocksource] 8901ecc231: stress-ng.lockbus.ops_per_sec -9.5%
 regression


> My current thought is that if more than (say) 100 consecutive attempts
> to read the clocksource get hit with excessive delays, it is time to at
> least do a WARN_ON(), and maybe also time to disable the clocksource
> due to skew.  The reason is that if reading the clocksource -always-
> sees excessive delays, perhaps the clock driver or hardware is to blame.
>
> Thoughts?

On TDX this would be fatal because we don't have a usable fallback source

(just jiffies). Better try as hard as possible.


-Andi

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