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Solarflare Server Adapter
User Guide
8.2 XenServer6 SR-IOV
Traditional Virtualization (without SR-IOV)
Traditional Xen paravirtualized networking involves bridging (paravirtualized) Netback devices to
physical network devices in dom0. The Netback driver interfaces with the Netfront driver running in
the guest, facilitating guest to guest connectivity.
Figure 54: Guest to Guest Connectivity
As a result of hardware virtualization, data copies between the Netfront driver in the guest and the
Netback driver in dom0 within the XenServer host become the bottleneck to the performance of this
implementation.
Typical Virtualization (with SR-IOV)
In emerging SR-IOV solutions PCIe hardware virtual functions (VF) allow a single network hardware
device to appear as multiple virtualized network devices to dom0. These virtualized network devices
operate independently of one another and present characteristics of actual physical devices to
dom0.
Using SR-IOV, a VF is passed-through to the guest operating system, and the guest network driver
binds directly to this PCIe VF, allowing the guest to bypass dom0 and providing direct access to the
network adapter from the guest VM. Direct access to the network hardware means that overheads
associated with dom0-based networking (virtualization, data copies, etc.) are eliminated, providing
significantly improved performance, see
Figure 55 .
However, a significant downside of this approach is that XenServer blocks migration of a VM when
a VF is present, which significantly reduces the functionality of server virtualization.