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

["Paul E. McKenney" <paulmck@kernel.org>]

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@rtptest1029.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