sudden appearance of timekeeping problems with netbsd-8 just after 8.1

[Greg Troxel <gdt%lexort.com@localhost>]

I have a fairly normal amd64 computer that I've been using for several
months without issues, tracking netbsd-8.  Until Sunday I was running
8.1_RC1 built on May 15.  I updated to 8.1_STABLE built from sources on
June 3.

Now, everything seems ok, except the system clock is losing massive
amounts of time.  Over 31.25 minutes of real time, the system clock
became behind 9 minutes.

ntpd is running, and is reporting offsets that are too big and too high
dispersion to syncrhonize.  The stored drift value is 18, which is
reasonable and does not explain this.

The machine is I think about 5 years old and has 4 cpus (cpucutl
identify at end) the following.  I am loading the new firmware at boot,
but I think that the problem began with the new kernel.

Diffing the dmesg from older netbsd-8 (built March 3, just because I
have that dmesg handy), and ignoring things that don't seem relevant:

  -timecounter: Timecounter "ACPI-Safe" frequency 3579545 Hz quality 900
  +timecounter: Timecounter "ACPI-Fast" frequency 3579545 Hz quality 1000

  -timecounter: Timecounter "TSC" frequency 2800071320 Hz quality 3000
  +timecounter: Timecounter "TSC" frequency 3920113160 Hz quality 3000

  +cpu 0: ucode 0x11->0x1d
  +cpu 1: ucode 0x11->0x1d
  +cpu 2: ucode 0x11->0x1d
  +cpu 3: ucode 0x11->0x1d

I have no memory of changing BIOS settings, but it seems there is
perhaps some variable clock rate thing going on, so that TSC is not what
it should be.  Or perhaps it's just miscalibrated.

I then set:
  kern.timecounter.hardware = hpet0
and things seem ok, at least after 10 minutes.

Is anyone else seeing this?

cpu0: highest basic info 0000000b
cpu0: highest extended info 80000008
cpu0: "Intel(R) Core(TM) i7 CPU         930  @ 2.80GHz"
cpu0: Intel Core i7, Xeon 34xx, 35xx and 55xx (Nehalem) (686-class), 3920.11 MHz
cpu0: family 0x6 model 0x1a stepping 0x5 (id 0x106a5)
cpu0: features 0xbfebfbff<FPU,VME,DE,PSE,TSC,MSR,PAE,MCE,CX8,APIC,SEP,MTRR,PGE>
cpu0: features 0xbfebfbff<MCA,CMOV,PAT,PSE36,CLFLUSH,DS,ACPI,MMX,FXSR,SSE,SSE2>
cpu0: features 0xbfebfbff<SS,HTT,TM,SBF>
cpu0: features1 0x98e3bd<SSE3,DTES64,MONITOR,DS-CPL,VMX,EST,TM2,SSSE3,CX16>
cpu0: features1 0x98e3bd<xTPR,PDCM,SSE41,SSE42,POPCNT>
cpu0: features2 0x28100800<SYSCALL/SYSRET,XD,RDTSCP,EM64T>
cpu0: features3 0x1<LAHF>
cpu0: features7 0x9c000000<IBRS,STIBP,L1D_FLUSH,SSBD>
cpu0: I-cache 32KB 64B/line 4-way, D-cache 32KB 64B/line 8-way
cpu0: L2 cache 256KB 64B/line 8-way
cpu0: L3 cache 8MB 64B/line 16-way
cpu0: 64B prefetching
cpu0: ITLB 128 4KB entries 4-way, 2M/4M: 7 entries
cpu0: DTLB 64 4KB entries 4-way, 2M/4M: 32 entries (L0)
cpu0: L2 STLB 512 4KB entries 4-way
cpu0: Initial APIC ID 0
cpu0: Cluster/Package ID 0
cpu0: Core ID 0
cpu0: SMT ID 0
cpu0: MONITOR/MWAIT extensions 0x3<EMX,IBE>
cpu0: monitor-line size 64
cpu0: C1 substates 2
cpu0: C2 substates 1
cpu0: C3 substates 1
cpu0: DSPM-eax 0x3<DTS,IDA>
cpu0: DSPM-ecx 0x1<HWF>
cpu0: SEF highest subleaf 00000000
cpu0: Perfmon-eax 0x7300403<VERSION=0x3,GPCounter=0x4,GPBitwidth=0x30>
cpu0: Perfmon-eax 0x7300403<Vectorlen=0x7>
cpu0: Perfmon-ebx 0x44<REFCYCL,BRMISPRRETR>
cpu0: Perfmon-edx 0x603<FixedFunc=0x3,FFBitwidth=0x30>
cpu0: microcode version 0x1d, platform ID 1