On 11/23/20 3:03 PM, Daniel P. Berrangé wrote:
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.
Don't NVMes live on a PCI(e) bus? Can't we just threat NVMes as PCI
devices? Or are we targeting sata too? Bcause we also have that type of
address.
Michal
