From: Thomas Gleixner <tglx@linutronix.de>
To: Feng Tang <feng.tang@intel.com>,
Xing Zhengjun <zhengjun.xing@linux.intel.com>,
paulmck@kernel.org
Cc: paulmck@kernel.org, John Stultz <john.stultz@linaro.org>,
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>,
Chris Mason <clm@fb.com>, LKML <linux-kernel@vger.kernel.org>,
lkp@lists.01.org, lkp@intel.com
Subject: Re: [LKP] Re: [clocksource] 6c52b5f3cf: stress-ng.opcode.ops_per_sec -14.4% regression
Date: Fri, 23 Apr 2021 21:09:58 +0200 [thread overview]
Message-ID: <87wnssvmux.ffs@nanos.tec.linutronix.de> (raw)
In-Reply-To: <20210422074126.GA85095@shbuild999.sh.intel.com>
On Thu, Apr 22 2021 at 15:41, Feng Tang wrote:
> On Thu, Apr 22, 2021 at 02:58:27PM +0800, Xing Zhengjun wrote:
>> It happened during boot and before TSC calibration
>> (tsc_refine_calibration_work()), so on some machines "abs(cs_nsec - wd_nsec)
>> > WATCHDOG_THRESHOLD", WATCHDOG_THRESHOLD is set too small at that time.
>> After TSC calibrated, abs(cs_nsec - wd_nsec) should be very small,
>> WATCHDOG_THRESHOLD for here is ok. So I suggest increasing the
>> WATCHDOG_THRESHOLD before TSC calibration, for example, the clocks be skewed
>> by more than 1% to be marked unstable.
>
> As Zhengjun measuered, this is a Cascade Lake platform, and it has 2
> times calibration of tsc, the first one of early quick calibration gives
> 2100 MHz, while the later accurate calibration gives 2095 MHz, so there
> is about 2.5/1000 deviation for the first number, which just exceeds the
> 1/1000 threshold you set :)
>
> Following is the tsc freq info from kernel log
>
> [ 0.000000] DMI: Intel Corporation S2600WFT/S2600WFT, BIOS SE5C620.86B.02.01.0008.031920191559 03/19/2019
> [ 0.000000] tsc: Detected 2100.000 MHz processor
> ...
> [ 13.859982] tsc: Refined TSC clocksource calibration: 2095.077 MHz
Right, that's because in 2021 we still use technology from the last
millenium to figure the correct TSC frequency out by doing a long time
measurement against some other timer where we assume to know the
frequeny it runs with.
Thanks,
tglx
prev parent reply other threads:[~2021-04-23 19:10 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-20 6:49 [clocksource] 6c52b5f3cf: stress-ng.opcode.ops_per_sec -14.4% regression kernel test robot
2021-04-20 13:43 ` Paul E. McKenney
2021-04-20 14:05 ` Paul E. McKenney
2021-04-21 6:07 ` [LKP] " Xing, Zhengjun
2021-04-21 13:42 ` Paul E. McKenney
2021-04-22 6:58 ` Xing Zhengjun
2021-04-22 7:41 ` Feng Tang
2021-04-22 14:24 ` Paul E. McKenney
2021-04-22 16:57 ` Paul E. McKenney
2021-04-23 6:11 ` Feng Tang
2021-04-23 14:02 ` Paul E. McKenney
2021-04-24 12:29 ` Feng Tang
2021-04-24 17:53 ` Paul E. McKenney
2021-04-25 2:14 ` Feng Tang
2021-04-25 3:14 ` Feng Tang
2021-04-25 19:15 ` Paul E. McKenney
2021-04-25 19:14 ` Paul E. McKenney
2021-04-26 12:39 ` Thomas Gleixner
2021-04-26 14:05 ` Feng Tang
2021-04-26 14:33 ` Thomas Gleixner
2021-04-26 15:12 ` Feng Tang
2021-04-23 2:15 ` Xing Zhengjun
2021-04-23 4:12 ` Paul E. McKenney
2021-04-23 19:14 ` Thomas Gleixner
2021-04-23 21:14 ` Paul E. McKenney
2021-04-23 23:39 ` Paul E. McKenney
2021-04-23 19:09 ` Thomas Gleixner [this message]
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