Description of problem:

(Below details were shared by the customer).

o Incorrect TSC calibration for overclocked BCLK
o In case of platforms overclocked by bumping BCLK (bus frequency) one ends up with TSC impacted as well.

o On one such hardware that we've evaluated we've seen TSC go up from the nominal 3.4GHz to 3.502GHz. 
This was evidenced by the output of turbostat (see attachement).

o Due to the way the kernel performs TSC calibration, the discovered frequency is still the nominal 3.4GHz as shown by dmesg.
-----------------------------------------------------
> dmesg | grep "tsc: Detected"
[    0.000000] tsc: Detected 3400.000 MHz processor
-----------------------------------------------------

o Modern kernels heavily rely on CPUID to obtain crystal frequency for the TSC (which for our Xeon 6246R SKU is 3.4GHz). With the actual frequency of TSC at 3502MHz the sfptp daemon will never be able to settle at stable freq adjust values and fail to synchronize the system clock against the NIC. Other kernel subsystems that rely on correctly identifying current frequency will also be impacted.

o This can be addressed by forcing the kernel to resort to using MSR rather than CPUID for obtaining TSC frequency in native_calibrate_cpu(void) (see attachement).

o Introducing additional kernel cmdline params to drive calibration method (ie. disabling cpuid as calibration source) would entirely solve this edge case without changing the default behaviour. Such change was successfully tested in customer's environments.

* Important Note:
o Customer has also given link of conversation in between Red Hat and Supermicro and wants to get follow up on the same.

https://lore.kernel.org/lkml/1543865843219.51523@supermicro.com/T/
OR https://marc.info/?t=153151085300010&r=1&w=2


* Request:
Is it possible to merge this patch in RHEL 8?


Version-Release number of selected component (if applicable):

RHEL 8.3.


How reproducible:
Customer has mentioned that it is always reproducible.


Steps to Reproduce:
Not known.


Actual results:
o overclocking impacts PTP clock synchronisation.

Expected results:
o Overclocking should not impact PTP clock synchronisation.

Additional info:
N/A.