[Bug 195819] TSC calibration can hang FreeBSD in Hyper-V Generation 2 VM

[bugzilla-noreply at freebsd.org]

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=195819

--- Comment #20 from Dexuan Cui <decui at microsoft.com> ---
FYI: in a Generation-1 Hyper-V FreeBSD 10.2 VM running on Hyper-V 2012 R2, the
tsc calibration by PIT seems broken:

dmesg shows
"
Calibrating TSC clock ... TSC clock: 1264483083 Hz
CPU: Intel(R) Xeon(R) CPU E5-2670 v2 @ 2.50GHz (1264.48-MHz K8-class CPU)
  Origin="GenuineIntel"  Id=0x306e4  Family=0x6  Model=0x3e  Stepping=4
 
Features=0x1f83fbff<FPU,VME,DE,PSE,TSC,MSR,PAE,MCE,CX8,APIC,SEP,MTRR,PGE,MCA,CMOV,PAT,PSE36,MMX,FXSR,SSE,SSE2,SS,HTT>
 
Features2=0xfe982203<SSE3,PCLMULQDQ,SSSE3,CX16,SSE4.1,SSE4.2,POPCNT,AESNI,XSAVE,OSXSAVE,AVX,F16C,RDRAND,HV>
 AMD Features=0x20100800<SYSCALL,NX,LM>
  AMD Features2=0x1<LAHF>
  Structured Extended Features=0x200<ERMS>
  XSAVE Features=0x1<XSAVEOPT>
"

We can see the 2.50GHz CPU is detected as 1.26G... It looks i8254_delay() may
not work properly somehow.

I tried to put "machdep.tsc_skip_calibration=1" in /boot/loader.conf, but it
looks this doesn't take effect -- anyone knows which loader config file I
should put the setting into?

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