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

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Message-ID: <Y4bxZCEAmPnALsRV@feng-clx>
Date:   Wed, 30 Nov 2022 14:00:04 +0800
From:   Feng Tang <feng.tang@...el.com>
To:     "Paul E. McKenney" <paulmck@...nel.org>
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 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 :)


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

Thanks,
Feng

> 							Thanx, Paul