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From: "Paul E. McKenney" <paulmck@kernel.org>
To: Chao Gao <chao.gao@intel.com>
Cc: Feng Tang <feng.tang@intel.com>,
	kernel test robot <oliver.sang@intel.com>,
	John Stultz <john.stultz@linaro.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Stephen Boyd <sboyd@kernel.org>, Jonathan Corbet <corbet@lwn.net>,
	Mark Rutland <Mark.Rutland@arm.com>,
	Marc Zyngier <maz@kernel.org>, Andi Kleen <ak@linux.intel.com>,
	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
Subject: Re: [clocksource]  8901ecc231:  stress-ng.lockbus.ops_per_sec -9.5% regression
Date: Thu, 5 Aug 2021 08:37:27 -0700	[thread overview]
Message-ID: <20210805153727.GG4397@paulmck-ThinkPad-P17-Gen-1> (raw)
In-Reply-To: <20210805053938.GA12593@gao-cwp>

On Thu, Aug 05, 2021 at 01:39:40PM +0800, Chao Gao wrote:
> [snip]
> >> This patch works well; no false-positive (marking TSC unstable) in a
> >> 10hr stress test.
> >
> >Very good, thank you!  May I add your Tested-by?
> 
> sure.
> Tested-by: Chao Gao <chao.gao@intel.com>

Very good, thank you!  I will apply this on the next rebase.

> >I expect that I will need to modify the patch a bit more to check for
> >a system where it is -never- able to get a good fine-grained read from
> >the clock.
> 
> Agreed.
> 
> >And it might be that your test run ended up in that state.
> 
> Not that case judging from kernel logs. Coarse-grained check happened 6475
> times in 43k seconds (by grep "coarse-grained skew check" in kernel logs).
> So, still many checks were fine-grained.

Whew!  ;-)

So about once per 13 clocksource watchdog checks.

To Andi's point, do you have enough information in your console log to
work out the longest run of course-grained clocksource checks?

> >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?
> 
> It makes sense to me.

Sounds good!

							Thanx, Paul

  reply	other threads:[~2021-08-05 15:37 UTC|newest]

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-21  8:33 kernel test robot
2021-05-21 13:56 ` Paul E. McKenney
2021-05-22 16:08   ` Paul E. McKenney
2021-05-26  6:49     ` Feng Tang
2021-05-26 13:49       ` Paul E. McKenney
2021-05-27 18:29         ` Paul E. McKenney
2021-05-27 19:01           ` Andi Kleen
2021-05-27 19:19             ` Paul E. McKenney
2021-05-27 19:29               ` Matthew Wilcox
2021-05-27 21:05                 ` Paul E. McKenney
2021-05-28  0:58                   ` Andi Kleen
2021-06-01 17:10                     ` Paul E. McKenney
2021-08-02  6:20           ` Chao Gao
2021-08-02 17:02             ` Paul E. McKenney
2021-08-03  8:58               ` Chao Gao
2021-08-03 13:48                 ` Paul E. McKenney
2021-08-05  2:16                   ` Chao Gao
2021-08-05  4:03                     ` Paul E. McKenney
2021-08-05  4:34                       ` Andi Kleen
2021-08-05 15:33                         ` Paul E. McKenney
2021-08-05  5:39                       ` Chao Gao
2021-08-05 15:37                         ` Paul E. McKenney [this message]
2021-08-06  2:10                           ` Chao Gao
2021-08-06  4:15                             ` Paul E. McKenney

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