Applying pve-qemu-kvm 10.2.1-1 may cause extremely high “I/O Delay” and extremely high “I/O pressure stalls”. (Patches in the test repository

martin_comp said:
I had to reboot the VMs (from Proxmox, not from within the VM).
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AFAIK, that is perfectly normal - as the new pve-qemu-kvm will only be applied on a host restart of the kvm, not internally by a VM reboot, which technically does not restart the kvm host-side.
 
I just wondered about this and had these thoughts:

When I migrate a VM from pve-node-1 to pve-node-2 it (and pve-node-2 has the patch) the patch will be applied and the problem is fixed without rebooting the VM from proxmox. Why cant proxmox then "upgrade" or "pass" the VM from the old pve-qemu-kvm to the newly installed pve-qemu-kvm ? The downtime (since internally passed, not through network) should be much lower than when "live-migrating".

This would prevent proxmox from needing to reboot the VMs, which I think would be a cool feature.

Does this make sense and it this possible?
 
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When you migrate the VM to another node, the new node is freshly starting the kvm instance (with the new pve-qemu-kvm version) - in fact it is also freshly "booting" the VM - as if it were just now booting - just the state (incl. RAM) has been saved (same as a hibernated system that is restarted).

Theoretically, on the same node - this could also be done by hibernating the VM (saving its state incl. RAM) & then restarting. Not sure what the time gain would be verses a complete clean reboot of the VM, although I guess this will be VM-dependent.
 
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