Messages in this thread | | | Date | Fri, 06 Dec 2019 16:13:05 +0000 | From | Krzysztof Piecuch <> | Subject | Re: [PATCH] x86/tsc: Don't use cpuid 0x16 leaf to determine cpu speed. |
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Thank you for your reply.
I experience 2% tsc clock-drift (671s ahead of my local NTP server after 9.5h) on my machine with Supermicro's Hyperspeed turned on. There's no clock drift when I turn Hyperspeed off.
As far as I know Hyperspeed increases base clock frequency[1].
That's what CPUID says about my overclocked Intel Xeon Gold 6146:
Time Stamp Counter/Core Crystal Clock Information (0x15): TSC/clock ratio = 256/2 nominal core crystal clock = 0 Hz Processor Frequency Information (0x16): Core Base Frequency (MHz) = 0xc80 (3200) Core Maximum Frequency (MHz) = 0x1068 (4200) Bus (Reference) Frequency (MHz) = 0x64 (100)
tsc_refine_calibration_work never corrects the early calibration because it calculates a tsc frequency beyond 1% tolerance.
I've bumped the tsc_refine_calibration_work's tolerance to 3% and made it work:
Hyperspeed: [ 8.571471] tsc: Refined TSC clocksource calibration: 3264.012 MHz No hyperspeed: [ 8.506009] tsc: Refined TSC clocksource calibration: 3200.013 MHz
Increasing the tolerance to 3% would work in my case but apparently some servers can increase the base-clock frequency to 6%. [2] At this point in order to completely eliminate this bug we would need to significantly increase the tolerance which might introduce other bugs.
[1]: https://www.supermicro.com/support/faqs/faq.cfm?faq=21337 [2]: https://www.servethehome.com/supermicro-hyper-speed-server-overclocking-bios/
Kind regards, Krzysztof Piecuch
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