Re: [libvirt] [Qemu-devel] [RFC v2] libvirt vGPU QEMU integration

Hi libvirt experts, Thanks for valuable input on v1 version of RFC. Quick brief, VFIO based mediated device framework provides a way to virtualize their devices without SR-IOV, like NVIDIA vGPU, Intel KVMGT and IBM's channel IO. This framework reuses VFIO APIs for all the functionalities for mediated devices which are currently being used for pass through devices. This framework introduces a set of new sysfs files for device creation and its life cycle management. Here is the summary of discussion on v1: 1. Discover mediated device: As part of physical device initialization process, vendor driver will register their physical devices, which will be used to create virtual device (mediated device, aka mdev) to the mediated framework. Vendor driver should specify mdev_supported_types in directory format. This format is class based, for example, display class directory format should be as below. We need to define such set for each class of devices which would be supported by mediated device framework. --- mdev_destroy --- mdev_supported_types |-- 11 | |-- create | |-- name | |-- fb_length | |-- resolution | |-- heads | |-- max_instances | |-- params | |-- requires_group |-- 12 | |-- create | |-- name | |-- fb_length | |-- resolution | |-- heads | |-- max_instances | |-- params | |-- requires_group |-- 13 |-- create |-- name |-- fb_length |-- resolution |-- heads |-- max_instances |-- params |-- requires_group In the above example directory '11' represents a type id of mdev device. 'name', 'fb_length', 'resolution', 'heads', 'max_instance' and 'requires_group' would be Read-Only files that vendor would provide to describe about that type. 'create': Write-only file. Mandatory. Accepts string to create mediated device. 'name': Read-Only file. Mandatory. Returns string, the name of that type id.

'fb_length': Read-only file. Mandatory. Returns <number>{K,M,G}, size of framebuffer. 'resolution': Read-Only file. Mandatory. Returns 'hres x vres' format. Maximum supported resolution. 'heads': Read-Only file. Mandatory. Returns integer. Number of maximum heads supported.

'max_instance': Read-Only file. Mandatory. Returns integer. Returns maximum mdev device could be created at the moment when this file is read. This count would be updated by vendor driver. Before creating mdev device of this type, check if max_instance is > 0. 'params' Write-Only file. Optional. String input. Libvirt would pass the string given in XML file to this file and then create mdev device. Set empty string to clear params. For example, set parameter 'frame_rate_limiter=0' to disable frame rate limiter for performance benchmarking, then create device of type 11. The device created would have that parameter set by vendor driver.

The parent device would look like: <device> <name>pci_0000_86_00_0</name> <capability type='pci'> <domain>0</domain> <bus>134</bus> <slot>0</slot> <function>0</function> <capability type='mdev'> <!-- one type element per sysfs directory --> <type id='11'> <!-- one element per sysfs file roughly --> <name>GRID M60-0B</name> <attribute name='fb_length'>512M</attribute> <attribute name='resolution'>2560x1600</attribute> <attribute name='heads'>2</attribute> <attribute name='max_instances'>16</attribute> <attribute name='requires_group'>1</attribute> </type>

</capability> <product id='...'>GRID M60</product> <vendor id='0x10de'>NVIDIA</vendor> </capability> </device> 2. Create/destroy mediated device With above example, vGPU device XML would look like: <device> <name>my-vgpu</name> <parent>pci_0000_86_00_0</parent> <capability type='mdev'> <type id='11'/> <group>1</group> <params>'frame_rate_limiter=0'</params>

</capability> </device> 'type id' is mandatory. 'group' is optional. It should be a unique number in the system among all the groups created for mdev devices. Its usage is: - not needed if single vGPU device is being assigned to a domain. - only need to be set if multiple vGPUs need to be assigned to a domain and vendor driver have 'requires_group' file in type id directory. - if type id directory include 'requires_group' and user tries to assign multiple vGPUs to a domain without having <group> field in XML, it will create single vGPU. 'params' is optional field. User should set this field if extra parameters need to be set for a particular vGPU device. Libvirt don't need to parse these params. These are meant for vendor driver. Libvirt need to follow the sequence to create device: * Read /sys/../0000\:86\:00.0/11/max_instances. If it is greater than 0, then only proceed else fail. * Set extra params if 'params' field exist in device XML and 'params' file exist in type id directory echo "frame_rate_limiter=0" > /sys/../0000\:86\:00.0/11/params

* Autogenerate UUID * Create device: echo "$UUID:<group>" > /sys/../0000\:86\:00.0/11/create where <group> is optional. Group should be unique number among all the groups created for mdev devices. * Clear params, if set earlier: echo "" > /sys/../0000\:86\:00.0/11/params * To destroy device: echo $UUID > /sys/../0000\:86\:00.0/mdev_destroy 3. Start/stop mediated device No change or requirement for libvirt as this will be handled by open() and close() callbacks to vendor driver. In case of multiple devices and 'requires_group' set, this will be handled in 'first open()' and 'last close()' on device in that group. 4. Launch QEMU/VM Pass the mdev sysfs path to QEMU as vfio-pci device. For above vGPU device example: -device vfio-pci,sysfsdev=/sys/bus/mdev/devices/$UUID 5. QEMU/VM Shutdown sequence No change or requirement for libvirt. 6. VM Reset No change or requirement for libvirt as this will be handled via VFIO reset API and QEMU process will keep running as before. 7. Hot-plug It is same syntax to create a virtual device for hot-plug.