Installation guide

PCI devices which are backed on the physical PCI device by resources such as queues and register
sets.
Ad van t ag es o f SR - IO V
SR-IOV devices can share a single physical port with multiple virtual machines.
Virtual Functions have near-native performance and provide better performance than para-
virtualized drivers and emulated access. Virtual Functions provide data protection between virtual
machines on the same physical server as the data is managed and controlled by the hardware.
These features allow for increased virtual machine density on hosts within a data center.
SR-IOV is better able to utilize the bandwidth of devices with multiple guests.
13.2. Using SR-IOV
This section covers the use of PCI passthrough to assign a Virtual Function of an SR-IOV capable
multiport network card to a virtual machine as a network device.
SR-IOV Virtual Functions (VFs) can be assigned to virtual machines by adding a device entry in
<hostdev> with the vi rsh ed i t or vi rsh attach-d evi ce command. However, this can be
problematic because unlike a regular network device, an SR-IOV VF network device does not have a
permanent unique MAC address, and is assigned a new MAC address each time the host is rebooted.
Because of this, even if the guest is assigned the same VF after a reboot, when the host is rebooted
the guest determines its network adapter to have a new MAC address. As a result, the guest believes
there is new hardware connected each time, and will usually require re-configuration of the guest's
network settings.
libvirt-0.9.10 and newer contains the <interface type='hostdev'> interface device. Using this
interface device, lib virt will first perform any network-specific hardware/switch initialization indicated
(such as setting the MAC address, VLAN tag, or 802.1Qbh virtualport parameters), then perform the
PCI device assignment to the guest.
Using the <interface type='hostdev'> interface device requires:
an SR-IOV-capable network card,
host hardware that supports either the Intel VT-d or the AMD IOMMU extensions, and
the PCI address of the VF to be assigned.
Important
Assignment of an SR-IOV device to a virtual machine requires that the host hardware supports
the Intel VT-d or the AMD IOMMU specification.
To attach an SR-IOV network device on an Intel or an AMD system, follow this procedure:
Pro ced u re 13.1. At t ach an SR- IO V n et wo rk d evice o n an In t el o r AMD syst em
1. En ab le In t el VT- d o r t h e AMD IO MMU sp ecif icat io n s in t h e BIO S an d kern el
Red Hat Ent erp rise Linux 6 Virt ualiz at ion Host Configurat ion and G uest Inst allat ion G uide
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