[nova] iothread support with Libvirt

Laurent Dumont laurentfdumont at gmail.com
Thu Jan 6 23:44:23 UTC 2022


Out of curiosity, how are you passing the local storage to the VM? I would
also assume a performance hit when using a VM but local storage (instead of
Ceph, iscsi, nfs) should still perform well?

On Thu, Jan 6, 2022 at 5:44 PM Eric K. Miller <emiller at genesishosting.com>
wrote:

> > > no there is no way to enable them out of band of nova today.
> > > you technially could wrap the qemu binary wiht a script that inject
> > parmaters
> > > but that obviously would not be supported upstream.
> > > but that would be a workaround if you really needed it
> > >
> > > https://review.opendev.org/c/openstack/devstack/+/817075 is an
> > exmaple
> > > of such a script
>
> I created a modified version of your script to wrap the qemu-kvm
> executable, but when OpenStack starts the VM, Nova returns:
>
> 2022-01-06 16:15:24.758 6 ERROR nova.compute.manager libvirtError:
> internal error: Failed to probe QEMU binary with QMP: qemu-kvm.orig:
> -object iothread,id=iothread0: invalid option
>
> "-object iothread,id=iothread0" is the first argument.
>
> Our Libvirt/QEMU versions are:
> Compiled against library: libvirt 4.5.0
> Using library: libvirt 4.5.0
> Using API: QEMU 4.5.0
> Running hypervisor: QEMU 2.12.0
>
> I'm pretty sure these versions includes support for iothreads (for both
> QEMU as well as Libvirt).
>
> Is Libvirt doing some form of cross-check on the XML parameters with the
> running QEMU parameters that is incompatible with the wrapper perhaps?
>
> Eric
>
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