Re: [libvirt] [Qemu-devel] [PATCH v7 0/4] Add Mediated device support

On 09/02/2016 05:44 PM, Paolo Bonzini wrote: > > > On 02/09/2016 22:19, John Ferlan wrote: >> We don't have such a pool for GPU's (yet) - although I suppose they >> could just become a class of storage pools. >> >> The issue being nodedev device objects are not saved between reboots. >> They are generated on the fly. Hence the "create-nodedev' API - notice >> there's no "define-nodedev' API, although I suppose one could be >> created. It's just more work to get this all to work properly. > > It can all be made transient to begin with. The VM can be defined but > won't start unless the mdev(s) exist with the right UUIDs. > >>> After creating the vGPU, if required by the host driver, all the other >>> type ids would disappear from "virsh nodedev-dumpxml >>> pci_0000_86_00_0" too. >> >> Not wanting to make assumptions, but this reads as if I create one type >> 11 vGPU, then I can create no others on the host. Maybe I'm reading it >> wrong - it's been a long week. > > Correct, at least for NVIDIA. > >> PCI devices have the "managed='yes|no'" attribute as well. That's what >> determines whether the device is to be detached from the host or not. >> That's been something very painful to manage for vfio and well libvirt! > > mdevs do not exist on the host (they do not have a driver on the host > because they are not PCI devices) so they do need any management. At > least I hope that's good news. :) What's your definition of "management"? They don't need the same type of management as a traditional hostdev, but they certainly don't just appear by magic! :-) For standard PCI devices, the managed attribute says whether or not the device needs to be detached from the host driver and attached to vfio-pci. For other kinds of hostdev devices, we could decide that it meant something different. In this case, perhaps managed='yes' could mean that the vGPU will be created as needed, and destroyed when the guest is finished with it, and managed='no' could mean that we expect a vGPU to already exist, and just need starting. Or not. Maybe that's a pointless distinction in this case. Just pointing out the option...