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

From: Feng Tang <feng.tang@intel.com>
To: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>,
	<linux-kernel@vger.kernel.org>, <sboyd@kernel.org>,
	<corbet@lwn.net>, <Mark.Rutland@arm.com>, <maz@kernel.org>,
	<kernel-team@meta.com>, <ak@linux.intel.com>,
	<zhengjun.xing@intel.com>, Chris Mason <clm@meta.com>,
	John Stultz <jstultz@google.com>,
	Waiman Long <longman@redhat.com>
Subject: Re: [PATCH clocksource 1/3] clocksource: Reject bogus watchdog clocksource measurements
Date: Wed, 30 Nov 2022 14:00:04 +0800	[thread overview]
Message-ID: <Y4bxZCEAmPnALsRV@feng-clx> (raw)
In-Reply-To: <20221130055024.GM4001@paulmck-ThinkPad-P17-Gen-1>

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