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Re: Question about migration of a VM between hosts having slight differe

From: Veselina Radeva
Subject: Re: Question about migration of a VM between hosts having slight difference in TSC Frequency
Date: Thu, 17 Dec 2020 18:48:42 +0200

Hi Lukas,

I using Libvirt `snapshot-create-as` and then `restore`. On restore I get the following errors:

qemu-system-x86_64: warning: TSC frequency mismatch between VM (3191999 kHz) and host (3191998 kHz), and TSC scaling unavailable

qemu-system-x86_64: kvm_init_vcpu failed: Invalid argument

I’m using Fedora CoreOS version 33, qemu 5.1, libvirt 6.6


On Dec 17, 2020, at 6:17 PM, Lukas Straub <lukasstraub2@web.de> wrote:

On Thu, 17 Dec 2020 14:04:03 +0200
Veselina Radeva <vessy@st6.io> wrote:


I'm trying to migrate a VM from one host to another where there is a 1KHz
difference in the TSC frequency between hosts. This results in errors
caused by this warning
so migration fails. On the other hand, I can see few lines before that
there is a try to allow TSC frequency difference between host and VM if it
falls within the specified bounds. It seems like `KVM_SET_TSC_KHZ`succeeds
only when TSC Scaling is available
Practically this means that migration between hosts having difference in
TSC frequency, even when it falls within bounds, is possible only when TSC
scaling is available.

On the other hand, in libvirt,
is allowed if TSC frequency difference falls within bounds, no matter if
TSC scaling is enabled or not.

So, I was wondering is it intended not to allow migration between hosts
having differences in TSC frequency if TSC scaling is not available? Or is
it a bug?

Thanks in advance,
Veselina Radeva

AFAIK, this is just a warning. I get it too and migration works fine here. How exactly is migration failing for you?

Lukas Straub


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