[pve-devel] Greatest common cluster cpuflags?

Alexandre DERUMIER aderumier at odiso.com
Tue Sep 24 05:49:45 CEST 2013


If I remember, they are a qemu option at vm start, to test if cpuflags exists on host when starting, and stop the vm if a configured flag is missing.

If you have homegenous cluster:

-with exactly same processor : you can choose host
-with only intel or only amd, but different generation : you can choose the lowest cpu model of the generaton

-mix of amd and intel : you need to use qemu64/kvm64

Now what do you want exactly ? only a check before migration ?
----- Mail original ----- 

De: "Mark Casey" <markc at unifiedgroup.com> 
À: pve-devel at pve.proxmox.com 
Envoyé: Lundi 23 Septembre 2013 21:51:15 
Objet: [pve-devel] Greatest common cluster cpuflags? 

Hello everyone, 

I've read that considerable performance improvements can be achieved 
using a non-default kvm CPU with a VM due to the availability of 
additional flags and extension sets. However I understand that this can 
be troublesome for live-migration when cluster Nodes are not on 
homogenous hardware. My own environment specifies a specific CPU for one 
cluster that is homogenous (though I haven't benchmarked it against 
defaults), but I'm stuck with defaults for another cluster which is 
Intel/AMD-mixed and uses CPUs from two different generations. 

Would it be possible for Proxmox to track the available cpuflags of 
Nodes and store them in the shared cluster filesystem? I think this 
would allow for running VMs with a greater set of cpuflags than the 
default while reducing the chance of panic (or, whatever) during 
live-migration. It may also be possible to compare the flags that a VM 
was started with and warn if the user attempts to live-migrate it to a 
Node that was added since the VM was last started (a Node which may 
support fewer flags than the other Nodes, causing problems). 

I have some interest in playing with this and (I think) a decent idea of 
the scope of work required. Would this idea be considered simply 
impossible, not likely to be adopted/merged under any circumstances, or 
just currently too dangerous without extensive testing? I'm not looking 
for anyone to do my homework for me or write me back a novel...but I 
don't want to waste time if it for sure won't go anywhere. :D 

Thank you, 
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