KVM Forum 2021

vDPA (virtio Data Path Acceleration) is a novel framework designed to simplify the software stack for hardware acceleration of devices. A vDPA device provides a data path fully compliant with the virtio specification which is suitable for implementation in hardware, and a vendor-specific control path. The abstraction provided by vDPA also makes software accelerators possible, similar to existing vhost or vhost-user devices.
Leveraging the potential of vDPA, Stefano will present a new vdpa-blk software device running in the host kernel that unifies hardware and software accelerators software stack. This new device draws on the experience with io_uring passthrough presented at the last KVM Forum, with a goal of achieving high performance. Accelerators bypass QEMU and therefore preclude the use of the features provided by QEMU block layer, such as image formats (e.g qcow2), I/O throttling, snapshots, etc. To keep using these features, Stefano will discuss an idea to detect when block layer functionality is needed and automatically use it with hardware or software vdpa-blk accelerators, leveraging the device emulation provided by QEMU.