linux-kernel - Re: [PATCH clocksource 1/3] clocksource: Reject bogus watchdog clocksource measurements

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Date:   Thu, 1 Dec 2022 09:24:05 -0800
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Feng Tang <feng.tang@...el.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>, linux-kernel@...r.kernel.org,
        sboyd@...nel.org, corbet@....net, Mark.Rutland@....com,
        maz@...nel.org, kernel-team@...a.com, ak@...ux.intel.com,
        zhengjun.xing@...el.com, Chris Mason <clm@...a.com>,
        John Stultz <jstultz@...gle.com>,
        Waiman Long <longman@...hat.com>
Subject: Re: [PATCH clocksource 1/3] clocksource: Reject bogus watchdog
 clocksource measurements

On Wed, Nov 30, 2022 at 02:00:04PM +0800, Feng Tang wrote:
> On Tue, Nov 29, 2022 at 09:50:24PM -0800, Paul E. McKenney wrote:
> [...]
> > >  
> > > Great! As both HPET and PM_TIMER get the same calibration 1975.000 MHz,
> > > and it matches the 40ms drift per second you mentioned earlier, this
> > > seems like the CPUID(0x15) gave the wrong frequence number.
> > > 
> > > Or unlikely, HPET and PM_TIMER are driven by the same circuit source,
> > > which has deviation.
> > > 
> > > Either way, I think the HW/FW could have some problem.
> > 
> > And this time with your printk()s:
> > 
> > [    0.000000] tsc: using CPUID[0x15] crystal_khz= 24000 kHz ebx=158 eax=2
> > [    0.000000] tsc: Detected 1900.000 MHz processor
> > [    0.000000] tsc: Detected 1896.000 MHz TSC
> > [    5.268858] clocksource: refined-jiffies: mask: 0xffffffff max_cycles: 0xffffffff, max_idle_ns: 1910969940391419 ns
> > [   25.706231] clocksource: tsc-early: mask: 0xffffffffffffffff max_cycles: 0x36a8d32ce31, max_idle_ns: 881590731004 ns
> > [   32.223011] clocksource: jiffies: mask: 0xffffffff max_cycles: 0xffffffff, max_idle_ns: 1911260446275000 ns
> > [   57.823933] clocksource: Switched to clocksource tsc-early
> > [   58.144840] clocksource: acpi_pm: mask: 0xffffff max_cycles: 0xffffff, max_idle_ns: 2085701024 ns
> > [   63.613713] clocksource: tsc: mask: 0xffffffffffffffff max_cycles: 0x36a8d32ce31, max_idle_ns: 881590731004 ns
> > [   63.637323] clocksource: Switched to clocksource tsc
> > [   64.673579] tsc: Warning: TSC freq calibrated by CPUID/MSR differs from what is calibrated by HW timer, please check with vendor!!
> > [   64.703719] tsc: Previous calibrated TSC freq:        1896.000 MHz
> > [   64.716816] tsc: TSC freq recalibrated by [PM_TIMER]:         1974.999 MHz
> 
> This confirms the tsc frequency is calculated from CPUID(0x15).
> 
> > What would be good next steps to check up on the hardware and firmware?
> 
> Maybe raise it to vendor? I have no idea how to check thos black boxes :)

Done, but no high hopes here.  (What, me cynical?  Better believe it!!!)

> > (My next step involves a pillow, but will follow up tomorrow morning
> > Pacific Time.)
>  
> Really thanks for checking this through late night!

No problem, and I guess it is instead the day after tomorrow, but
I thought you might be interested in chronyd's opinion:

[root@...test1029.snc8 ~]# cat /var/lib/chrony/drift
        40001.074911             0.002098

In contrast, on my Fedora laptop:

$ sudo cat /var/lib/chrony/drift
            2.074313             0.186606

I am (perhaps incorrectly) taking this to indicate that TSC is in fact
drifting with respect to standard time.

Thoughts?

							Thanx, Paul