TSC-low wrong frequency slowing down time

kommissar · May 14, 2020

I noticed in the last boot up that my clock was slower than normal, ntp would not sync, and "sleep 10" would take over ten seconds of real wall clock time.

I debugged it down to TSC-low getting the wrong frequency. This fixed my problem:
sysctl kern.timecounter.hardware="HPET"

So I also put that in /etc/sysctl.conf

Looking at the last boot messages compared to older ones, I noticed this:

Code:

...
Apr 16 00:15:57 media kernel: Timecounter "TSC-low" frequency 1700046556 Hz quality 1000
Apr 24 15:11:17 media kernel: Timecounter "TSC-low" frequency 1700048888 Hz quality 1000
May  3 17:29:56 media kernel: Timecounter "TSC-low" frequency 1700049236 Hz quality 1000
May  9 00:17:54 media kernel: Timecounter "TSC-low" frequency 1700044866 Hz quality 1000
May 12 17:44:41 media kernel: Timecounter "TSC-low" frequency 1087886338 Hz quality 1000

So the TSC-low frequency was probably wrong on the last boot.

I also see this:

Code:

...
Apr 16 00:15:57 media kernel: CPU: Intel(R) Core(TM) i3-3245 CPU @ 3.40GHz (3400.09-MHz K8-class CPU)
Apr 24 15:11:17 media kernel: CPU: Intel(R) Core(TM) i3-3245 CPU @ 3.40GHz (3400.10-MHz K8-class CPU)
May  3 17:29:56 media kernel: CPU: Intel(R) Core(TM) i3-3245 CPU @ 3.40GHz (3400.10-MHz K8-class CPU)
May  9 00:17:54 media kernel: CPU: Intel(R) Core(TM) i3-3245 CPU @ 3.40GHz (3400.09-MHz K8-class CPU)
May 12 17:44:41 media kernel: CPU: Intel(R) Core(TM) i3-3245 CPU @ 3.40GHz (17406.18-MHz K8-class CPU)

Any idea what might cause this? IIRC the change I made in the last boot was installing a new case fan and telling the BIOS to throttle the fan speed based on CPU temperature. But this is not frequency scaling or anything I think should be visible to the operating system.

Any ideas on how to debug?

PMc · May 14, 2020

kommissar said:
Any idea what might cause this? IIRC the change I made in the last boot was installing a new case fan and telling the BIOS to throttle the fan speed based on CPU temperature. But this is not frequency scaling or anything I think should be visible to the operating system.

It sound like that BIOS got something seriously wrong during these changes, and now reports the wrong stuff up to the OS.

Any ideas on how to debug?

Debugging the BIOS? Hm, that sounds quite difficult to me. What I would do is, if that doesn't go away by itself during the next BIOS edit anyway, one can do a reset of the BIOS (and then recreate the config) - the mainboard manual should explain that.

kommissar · May 17, 2020

PMc said:
It sound like that BIOS got something seriously wrong during these changes, and now reports the wrong stuff up to the OS.

I don't think that it is actually the BIOS reporting this. After a reboot, the frequency is reported properly again, and things are working.

Code:

May  9 00:17:54 media kernel: Timecounter "TSC-low" frequency 1700044866 Hz quality 1000
May 12 17:44:41 media kernel: Timecounter "TSC-low" frequency 1087886338 Hz quality 1000
May 16 23:04:56 media kernel: Timecounter "TSC-low" frequency 1700046370 Hz quality 1000

Usually, there is some sort of calibration in the kernel. I thought maybe there is a bug there. But if this is a transient issue, it will be much more difficult to figure out.