Single Root I/O Virtualization (SR-IOV) – Part 1

The single root I/O virtualization (SR-IOV) interface is an extension to the PCI Express (PCIe) specification. SR-IOV allows a device, such as a network adapter, to separate access to its resources among various PCIe hardware functions. These functions consist of the following types:

  • A PCIe Physical Function (PF). This function is the primary function of the device and advertises the device’s SR-IOV capabilities. The PF is associated with the Hyper-V parent partition in a virtualized environment.
  • One or more PCIe Virtual Functions (VFs). Each VF is associated with the device’s PF. A VF shares one or more physical resources of the device, such as a memory and a network port, with the PF and other VFs on the device. Each VF is associated with a Hyper-V child partition in a virtualized environment.

Each PF and VF is assigned a unique PCI Express Requester ID (RID) that allows an I/O memory management unit (IOMMU) to differentiate between different traffic streams and apply memory and interrupt translations between the PF and VFs. This allows traffic streams to be delivered directly to the appropriate Hyper-V parent or child partition. As a result, nonprivileged data traffic flows from the PF to VF without affecting other VFs.

SR-IOV enables network traffic to bypass the software switch layer of the Hyper-V virtualization stack. Because the VF is assigned to a child partition, the network traffic flows directly between the VF and child partition. As a result, the I/O overhead in the software emulation layer is diminished and achieves network performance that is nearly the same performance as in nonvirtualized environments.

SR-IOV Architecture

Hyper-V Extensible Switch Module

The extensible switch module that configures the NIC switch on the SR-IOV network adapter to provide network connectivity to the Hyper-V child partitions.

Note  Hyper-V child partitions are known as virtual machines (VMs).

If the child partitions are connected to a PCI Express (PCIe) Virtual Function (VF), the extensible switch module does not participate in data traffic between the VM and the network adapter. Instead, data traffic is passed directly between the VM and the VF to which it is attached.

Physical Function (PF)

The PF is a PCI Express (PCIe) function of a network adapter that supports the SR-IOV interface. The PF includes the SR-IOV Extended Capability in the PCIe Configuration space. The capability is used to configure and manage the SR-IOV functionality of the network adapter, such as enabling virtualization and exposing VFs.

For more information, see SR-IOV Physical Function (PF).

PF Miniport Driver

The PF miniport driver is responsible for managing resources on the network adapter that are used by one or more VFs. Because of this, the PF miniport driver is loaded in the management operating system before any resources are allocated for a VF. The PF miniport driver is halted after all resources that were allocated for VFs are freed.

Virtual Function (VF)

A VF is a lightweight PCIe function on a network adapter that supports the SR-IOV interface. The VF is associated with the VF on the network adapter, and represents a virtualized instance of the network adapter. Each VF has its own PCI Configuration space. Each VF also shares one or more physical resources on the network adapter, such as an external network port, with the PF and other VFs.

For more information, see SR-IOV Virtual Functions (VFs).

VF Miniport Driver

The VF miniport driver is installed in the VM to manage the VF. Any operation that is performed by the VF miniport driver must not affect any other VF or the PF on the same network adapter.

Network Interface Card (NIC) Switch

The NIC switch is a hardware component of the network adapter that supports the SR-IOV interface. The NIC switch forwards network traffic between the physical port on the adapter and internal virtual ports (VPorts). Each VPort is attached to either the PF or a VF.

Virtual Ports (VPorts)

A VPort is a data object that represents an internal port on the NIC switch of a network adapter that supports the SR-IOV interface. Similar to a port on a physical switch, a VPort on the NIC switch delivers packets to and from a PF or VF to which the port is attached.

Physical Port

The physical port is a hardware component of the network adapter that supports the SR-IOV interface. The physical port provides the interface on the adapter to the external networking medium.

For more information on SR-IOV, refer to the PCI-SIG Single Root I/O Virtualization and Sharing 1.1 specification.

Reference: Microsoft.com

Davoud Teimouri

Davoud Teimouri is as a professional blogger, vExpert 2015/2016/2017/2018/2019, VCA, MCITP. This blog is started with simple posts and now, it has large following readers.

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