Re: clock stability, TSC, and QEMU

[PHO <pho%cielonegro.org@localhost>]

On 5/9/21 3:23 PM, nia wrote:
> hello,
> 
> when running NetBSD as a QEMU guest, there seem to be problems
> with clock stability.
> 
> i remember having this problem when using a commercial KVM-based VM
> host. erlang is very sensitive to monotonic clock drift, and
> will abort if it detects it. my application would infrequently
> abort regardless of kern.timecounter.hardware (although ACPI-Safe
> annecdotally made it less worse) due to the monotonic clock
> stepping backwards.
> 
> when running NetBSD as a QEMU guest with NVMM, the following
> message is printed to dmesg on boot:
> 
> autoconfiguration ERROR: 9225914709 cycle TSC drift observed

Yeah, the same thing happens on NetBSD running as a VMWare Fusion guest
and a VirtualBox guest. I remember when I tried VirtualBox, the audio
driver it chose (I can't remember which one it was) frequently
malfunctioned apparently due to the clock instability. It looked like it
was waiting for an interrupt which wasn't supposed to happen at the
moment the driver expected.