Time drift using q35

[Ulrar]

Hi,

We've been installing machines for years on proxmox without any issues, but the other day I figured I'd try q35 since it's available, just by curiosity, and I installed a few virtual machines on a single node using it.

They seem to be working fine, but the time is drifting pretty fast and openntpd is struggling to keep up :


May 23 09:25:06 vs2 ntpd[31252]: adjusting local clock by 2.647355s
May 23 09:25:38 vs2 ntpd[31252]: adjusting local clock by 2.692527s
May 23 09:27:16 vs2 ntpd[31252]: adjusting local clock by 2.761033s
May 23 09:27:46 vs2 ntpd[31252]: adjusting local clock by 2.884207s


I've never seen that before in a VM, and the only difference I can think of is that those VMs are using q35. Anyone experienced that ?
The clock source is kvm-clock as usual, and the qemu-guest-agent is installed if that matters.

 

[wolfgang]

Hi,

in a VM you have always the problem of time drifts.
This is the reason why every Hypervisor vendor recommends to use an external timer like a NTP server

 

[Ulrar]

Of course, but you're talking about a few seconds a day at most, and that is the behavior with the default chipset indeed.
But using q35 we're talking about multiple minutes per hour, that's a drift of something like half an hour per day, that can't be normal.

And that's under no load, of course, just empty virtual machines.

 

[wolfgang]

Do you have bost and power saving in the bios active?
Because this could also a reason for this.

 

[Ulrar]

I don't actually know how to get into the BIOS of a VM ? Does that even make sense ?

 

[wolfgang]

I meant the host bios.
It is true that q35 has the other time implementation as i440fx but the source of the problem is the same.

 

[Ulrar]

It's OVH, I don't have access to the host BIOS.
But i440fx works perfectly fine, that problem only occurs with q35