Windows Server 2012 : Increase scalability and performance (part 2) - Network adapter hardware acceleration

Virtual Machine Queue (VMQ) was first available for the Hyper-V role in Windows Server 2008 R2 for host machines that had VMQ-capable network adapter hardware. VMQ employs hardware packet filtering to deliver packets from an external VM network directly to VMs using Direct Memory Access (DMA) transfers. This helps reduce the overhead of routing packets from the host to the VM, which helps improve the performance of the host operating system by distributing the processing of network traffic for multiple VMs among multiple processors. Previously, all network traffic was handled by a single processor.

Figure 2. Enabling use of the hardware acceleration capabilities of high-end network adapter hardware on Hyper-V hosts.

NDIS 6.30 in Windows Server 2012 includes some changes and enhancements in how VMQ is implemented. For example, splitting network data into separate look-ahead buffers is no longer supported.

Although in Windows Server 2008 R2 you had to use System Center Virtual Machine Manager to enable VMQ for a VM on a Hyper-V host, beginning with Windows Server 2012, you can enable VMQ directly from within the VM’s settings exposed through Hyper-V Manager, as discussed previously.

Internet Protocol Security (IPsec) task offload was first available for servers running Windows Server 2008 that had network adapters that supported this functionality. IPsec task offload works by reducing the load on the system’s processors by performing the computationally intensive job of IPsec encryption/decryption using a dedicated processor on the network adapter. The result can be a dramatically better use of the available bandwidth for an IPsec-enabled computer.

Beginning with Windows Server 2012, you can enable IPsec task offload directly from within the VM’s settings exposed through Hyper-V Manager, as detailed previously.

Single root I/O virtualization (SR-IOV) is an extension to the PCI Express (PCIe) specification, which enables a device such as a network adapter to divide access to its resources among various PCIe hardware functions. As implemented in the Hyper-V role of Windows Server 2012, SR-IOV enables network traffic to bypass the software switch layer of the Hyper-V virtualization stack to reduce the I/O overhead in this layer. By assigning SR-IOV capable devices directly to a VM, the network performance of the VM can be nearly as good as that of a physical machine. In addition, the processing overhead on the host is reduced.

Beginning with Windows Server 2012, you can enable SR-IOV directly from within the VM’s settings exposed through Hyper-V Manager, as shown in Figure 3. Before you can do this, however, the virtual switch that the VM uses must have SR-IOV enabled on it, and you also may need to install additional network drivers in the guest operating system of the VM. Note that you can enable SR-IOV on a virtual switch only when you create the switch using the Virtual Switch Manager of Hyper-V Manager or by using the New-VMSwitch cmdlet when using PowerShell.

Figure 3. SR-IOV must be configured on the virtual switch before it can be configured for the VM.