Re: Libvirt NVME support

On Wed, Nov 18, 2020 at 11:24:30AM +0100, Peter Krempa wrote: > On Wed, Nov 18, 2020 at 09:57:14 +0000, Thanos Makatos wrote: >>> As a separate question, is there any performance benefit of emulating a >>> NVMe controller compared to e.g. virtio-scsi? >> >> We haven't measured that yet; I would expect it to be slight faster and/or more >> CPU efficient but wouldn't be surprised if it isn't. The main benefit of using >> NVMe is that we don't have to install VirtIO drivers in the guest. > > Okay, I'm not sold on the drivers bit but that is definitely not a > problem in regards of adding support for emulating NVME controllers to > libvirt. > > As a starting point a trivial way to model this in the XML will be: > > <controller type='nvme' index='1' model='nvme'> > > And then add the storage into it as: > > <disk type='file' device='disk'> > <source dev='/Host/QEMUGuest1.qcow2'/> > <target dev='sda' bus='nvme'/> > <address type='drive' controller='1' bus='0' target='0' unit='0'/> > </disk> > > <disk type='file' device='disk'> > <source dev='/Host/QEMUGuest2.qcow2'/> > <target dev='sdb' bus='nvme'/> > <address type='drive' controller='1' bus='0' target='0' unit='1'/> > </disk> > > The 'drive' address here maps the disk to the controller. This example > uses unit= as the way to specify the namespace ID. Both 'bus' and 'target' > must be 0. FWIW, I think that our overloeading of type=drive for FDC, IDE, and SCSI was a mistake in retrospect. We should have had type=fdc, type=ide, type=scsi, since each uses a different subset of the attributes. Lets not continue this mistake with NVME - create a type=nvme address type.