SR-IOV enables a Single Root Function (for example, a single Ethernet port), to appear as multiple, separate, physical devices. A physical device with SR-IOV capabilities can be configured to appear in the PCI configuration space as multiple functions, each device has its own configuration space complete with Base Address Registers (BARs).
SR-IOV uses two new PCI functions:
- Physical Functions (PFs) are full PCIe devices that include the SR-IOV capabilities. Physical Functions are discovered, managed, and configured as normal PCI devices. Physical Functions configure and manage the SR-IOV functionality by assigning Virtual Functions.
- Virtual Functions (VFs) are simple PCIe functions that only process I/O. Each Virtual Function is derived from a Physical Function. The number of Virtual Functions a device may have is limited by the device hardware. A single Ethernet port, the Physical Device, may map to many Virtual Functions that can be shared to guests.
The hypervisor can map one or more Virtual Functions to a guest. The Virtual Function's configuration space is mapped, by the hypervisor, to the guest's configuration space.
Each Virtual Function can only be mapped once as Virtual Functions require real hardware. A guest can have multiple Virtual Functions. A Virtual Function appears as a network card in the same way as a normal network card would appear to an operating system.
The SR-IOV drivers are implemented in the kernel. The core implementation is contained in the PCI subsystem, but there must also be driver support for both the Physical Function (PF) and Virtual Function (VF) devices. With an SR-IOV capable device one can allocate VFs from a PF. The VFs appear as PCI devices which are backed on the physical PCI device by resources (queues, and register sets).
Note
For optimal performance, refer to Performance Tuning of VMs page before preceding with the information in this section.
Prerequisites
Install Linux Vanilla flavor 7.2
- Install SRIOV supported PCI card
- Enable VT-d / IOMMU in BIOS
Configure the Linux Vanilla flavor kernel to support IOMMU.
Procedure
Log on to the Host IP as root user.
To know the maximum number of virtual functions a physical function can support, execute below command:
cat /sys/class/net/eth3/device/sriov_totalvfs
On a host machine (compute node), create the required number of virtual functions via the PCI SYS interface. Execute below command:
In this example, we create 8 virtual functions. The total number of virtual functions is based on the requirements.echo "echo '8' > /sys/class/net/eth3/device/sriov_numvfs" >> /etc/rc.local
Execute the following command:
chmod +x /etc/rc.d/rc.local
Reboot the system.
To verify devices exist and to attach VM:
To list the newly added Virtual functions attached to the network device, execute below command:
Example: Intel I350lspci | grep I350 01:00.0 Ethernet controller: Intel Corporation I350 Gigabit Network Connection (rev 01) 01:00.1 Ethernet controller: Intel Corporation I350 Gigabit Network Connection (rev 01) 01:00.2 Ethernet controller: Intel Corporation I350 Gigabit Network Connection (rev 01) 01:00.3 Ethernet controller: Intel Corporation I350 Gigabit Network Connection (rev 01) 01:00.4 Ethernet controller: Intel Corporation I350 Gigabit Network Connection (rev 01) 01:00.5 Ethernet controller: Intel Corporation I350 Gigabit Network Connection (rev 01) 01:00.6 Ethernet controller: Intel Corporation I350 Gigabit Network Connection (rev 01) 01:00.7 Ethernet controller: Intel Corporation I350 Gigabit Network Connection (rev 01) 01:10.0 Ethernet controller: Intel Corporation I350 Ethernet Controller Virtual Function (rev 01) 01:10.1 Ethernet controller: Intel Corporation I350 Ethernet Controller Virtual Function (rev 01) 01:10.2 Ethernet controller: Intel Corporation I350 Ethernet Controller Virtual Function (rev 01) 01:10.3 Ethernet controller: Intel Corporation I350 Ethernet Controller Virtual Function (rev 01) 01:10.4 Ethernet controller: Intel Corporation I350 Ethernet Controller Virtual Function (rev 01) 01:10.5 Ethernet controller: Intel Corporation I350 Ethernet Controller Virtual Function (rev 01) 01:10.6 Ethernet controller: Intel Corporation I350 Ethernet Controller Virtual Function (rev 01) 01:10.7 Ethernet controller: Intel Corporation I350 Ethernet Controller Virtual Function (rev 01)
To filter the Intel I350 network device from the list of available host devices use 01, execute below command:
virsh nodedev-list | grep 01 pci_0000_01_00_0 pci_0000_01_00_1 pci_0000_01_00_2 pci_0000_01_00_3 pci_0000_01_00_4 pci_0000_01_00_5 pci_0000_01_00_6 pci_0000_01_00_7 pci_0000_01_10_0 pci_0000_01_10_1 pci_0000_01_10_2 pci_0000_01_10_3 pci_0000_01_10_4 pci_0000_01_10_5 pci_0000_01_10_6 pci_0000_01_10_7
To get device details:
Follow step 6 and 7 for other packet interface as well.
The pci_0000_01_00_0 is one of the Physical Functions and pci_0000_01_10_0 is the first corresponding Virtual Function for that Physical Function.
To get advanced output for both devices, execute below command:
virsh nodedev-dumpxml pci_0000_01_10_0 <device> <name>pci_0000_01_10_0</name> <path>/sys/devices/pci0000:00/0000:00:03.0/0000:01:10.0</path> <parent>pci_0000_00_03_0</parent> <driver> <name>igbvf</name> </driver> <capability type='pci'> <domain>0</domain> <bus>1</bus> <slot>16</slot> <function>0</function> <product id='0x1520'>I350 Ethernet Controller Virtual Function</product> <vendor id='0x8086'>Intel Corporation</vendor> <capability type='phys_function'> <address domain='0x0000' bus='0x01' slot='0x00' function='0x2'/> </capability> <iommuGroup number='94'> <address domain='0x0000' bus='0x01' slot='0x10' function='0x2'/> </iommuGroup> <numa node='0'/> <pci-express> <link validity='cap' port='0' speed='5' width='4'/> <link validity='sta' width='0'/> </pci-express> </capability> </device>This example adds the Virtual Function pci_0000_01_10_0 to the virtual machine. Note the bus, slot and function parameters of the Virtual Function is required for adding the device. For example, copy these parameters into a temporary XML file, such as /tmp/new-interface.xml.
<interface type='hostdev' managed='yes'> <source> <address type='pci' domain='0' bus='1' slot='16' function='0'/> </source> </interface>
Before going to add the Virtual Functions to the virtual machine, we must detach those virtual functions from Host machine.
virsh nodedev-detach pci_0000_01_10_0
- Before you proceed with the below step, create virtual machine. Refer to Creating a New SBC SWe Instance on KVM Hypervisor.
To add the Virtual Function to the virtual machine, execute below command. This attaches the new device immediately and saves it for subsequent guest restarts.
The MyGuest indicates the Virtual Machine name.
virsh attach-device [MyGuest] /tmp/new-interface.xml --config
Using the --config option ensures the new device is available after future guest restarts.
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