| .. SPDX-License-Identifier: GPL-2.0-or-later |
| |
| Compsable SR-IOV device |
| ======================= |
| |
| SR-IOV (Single Root I/O Virtualization) is an optional extended capability of a |
| PCI Express device. It allows a single physical function (PF) to appear as |
| multiple virtual functions (VFs) for the main purpose of eliminating software |
| overhead in I/O from virtual machines. |
| |
| There are devices with predefined SR-IOV configurations, but it is also possible |
| to compose an SR-IOV device yourself. Composing an SR-IOV device is currently |
| only supported by virtio-net-pci. |
| |
| Users can configure an SR-IOV-capable virtio-net device by adding |
| virtio-net-pci functions to a bus. Below is a command line example: |
| |
| .. code-block:: shell |
| |
| -netdev user,id=n -netdev user,id=o |
| -netdev user,id=p -netdev user,id=q |
| -device pcie-root-port,id=b |
| -device virtio-net-pci,bus=b,addr=0x0.0x3,netdev=q,sriov-pf=f |
| -device virtio-net-pci,bus=b,addr=0x0.0x2,netdev=p,sriov-pf=f |
| -device virtio-net-pci,bus=b,addr=0x0.0x1,netdev=o,sriov-pf=f |
| -device virtio-net-pci,bus=b,addr=0x0.0x0,netdev=n,id=f |
| |
| The VFs specify the paired PF with ``sriov-pf`` property. The PF must be |
| added after all VFs. It is the user's responsibility to ensure that VFs have |
| function numbers larger than one of the PF, and that the function numbers |
| have a consistent stride. Both the PF and VFs are ARI-capable so you can have |
| 255 VFs at maximum. |
| |
| You may also need to perform additional steps to activate the SR-IOV feature on |
| your guest. For Linux, refer to [1]_. |
| |
| .. [1] https://docs.kernel.org/PCI/pci-iov-howto.html |
