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Message-ID: <20221202014428.GN4001@paulmck-ThinkPad-P17-Gen-1>
Date: Thu, 1 Dec 2022 17:44:28 -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 Fri, Dec 02, 2022 at 09:10:12AM +0800, Feng Tang wrote:
> On Thu, Dec 01, 2022 at 09:24:05AM -0800, Paul E. McKenney wrote:
> > 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.
>
> This info is very useful! It further confirms the CPUID(0x15) gave
> the wrong frequency info.
So the TSC is just doing what it is told. ;-)
This indicates a firmware problem?
> Also I don't think TSC itself is drifting, and the drift some from
> the wrong match calculation(1896 MHz), if we give it the correct
> number (likely 1975 MHz here), there shouldn't be big chrony drift
> like your Fedora laptop.
Resetting so that the clocksource watchdog once again gets rid of TSC,
but leaving nohpet:
[ 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
[ 5.287750] clocksource: refined-jiffies: mask: 0xffffffff max_cycles: 0xffffffff, max_idle_ns: 1910969940391419 ns
[ 17.963947] clocksource: tsc-early: mask: 0xffffffffffffffff max_cycles: 0x36a8d32ce31, max_idle_ns: 881590731004 ns
[ 19.996287] clocksource: timekeeping watchdog on CPU3: Marking clocksource 'tsc-early' as unstable because the skew is too large:
[ 20.040287] clocksource: 'refined-jiffies' wd_nsec: 503923392 wd_now: fffb73f8 wd_last: fffb7200 mask: ffffffff
[ 20.067286] clocksource: 'tsc-early' cs_nsec: 588021368 cs_now: 581c1eb378 cs_last: 57d9aad9e8 mask: ffffffffffffffff
[ 20.096286] clocksource: No current clocksource.
[ 20.111286] tsc: Marking TSC unstable due to clocksource watchdog
[ 24.582541] clocksource: jiffies: mask: 0xffffffff max_cycles: 0xffffffff, max_idle_ns: 1911260446275000 ns
[ 49.739301] clocksource: Switched to clocksource refined-jiffies
[ 50.046356] clocksource: acpi_pm: mask: 0xffffff max_cycles: 0xffffff, max_idle_ns: 2085701024 ns
[ 50.066475] clocksource: Switched to clocksource acpi_pm
# cat /var/lib/chrony/drift
1.372570 0.020049
I interpret this to mean that acpi_pm (and thus from prior observations,
HPET as well) are counting at the correct rate.
Thanx, Paul
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