Re: [PATCH clocksource 1/3] clocksource: Reject bogus watchdog clocksource measurements
From: Feng Tang
Date: Thu Dec 01 2022 - 21:06:13 EST
On Thu, Dec 01, 2022 at 05:44:28PM -0800, Paul E. McKenney wrote:
> 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.
Correct. And this is a good news! that 1975 MHz seems to be the right
number.
Could you try below patch, it should override the CPUID calculation
and forced to use HW timer calibrated number:
---
diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index a78e73da4a74..68a2fea4961d 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -1417,7 +1417,8 @@ static int __init init_tsc_clocksource(void)
* When TSC frequency is known (retrieved via MSR or CPUID), we skip
* the refined calibration and directly register it as a clocksource.
*/
- if (boot_cpu_has(X86_FEATURE_TSC_KNOWN_FREQ)) {
+// if (boot_cpu_has(X86_FEATURE_TSC_KNOWN_FREQ)) {
+ if (false) {
if (boot_cpu_has(X86_FEATURE_ART))
art_related_clocksource = &clocksource_tsc;
clocksource_register_khz(&clocksource_tsc, tsc_khz);
---
And together with b50db7095fe0 "x86/tsc: Disable clocksource watchdog
for TSC on qualified platorms". I assume this will tell TSC to use
1975 MHZ as its frequency.
Thanks,
Feng