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Subject: Re: [clocksource] 8901ecc231: stress-ng.lockbus.ops_per_sec -9.5%
 regression
To:     paulmck@kernel.org, Chao Gao <chao.gao@intel.com>
Cc:     Feng Tang <feng.tang@intel.com>,
        kernel test robot <oliver.sang@intel.com>,
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        Thomas Gleixner <tglx@linutronix.de>,
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        Jonathan Corbet <corbet@lwn.net>,
        Mark Rutland <Mark.Rutland@arm.com>,
        Marc Zyngier <maz@kernel.org>,
        Xing Zhengjun <zhengjun.xing@linux.intel.com>,
        Chris Mason <clm@fb.com>, LKML <linux-kernel@vger.kernel.org>,
        Linux Memory Management List <linux-mm@kvack.org>,
        lkp@lists.01.org, lkp@intel.com, ying.huang@intel.com,
        zhengjun.xing@intel.com
References: <20210521135617.GT4441@paulmck-ThinkPad-P17-Gen-1>
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 <20210803085759.GA31621@gao-cwp>
 <20210803134816.GO4397@paulmck-ThinkPad-P17-Gen-1>
 <20210805021646.GA11629@gao-cwp>
 <20210805040349.GD4397@paulmck-ThinkPad-P17-Gen-1>
From:   Andi Kleen <ak@linux.intel.com>
Message-ID: <a8d99be8-da3f-6c8e-cdbb-efd239ff3f14@linux.intel.com>
Date:   Wed, 4 Aug 2021 21:34:13 -0700
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> 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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