I/O Domain Overview

An I/O domain has direct ownership of and direct access to physical I/O devices. It can be created by assigning a PCI EXPRESS (PCIe) bus or a PCIe endpoint device to a domain. Use the ldm add-io command to assign a bus or device to a domain.

You might want to configure I/O domains for the following reasons:

• An I/O domain has direct access to a physical I/O device, which avoids the performance overhead that is associated with virtual I/O. As a result, the I/O performance on an I/O domain more closely matches the I/O performance on a bare-metal system.

• An I/O domain can host virtual I/O services to be used by other guest domains.

For information about configuring I/O domains, see the following:

• Assigning PCIe Buses

• Assigning PCIe Endpoint Devices

General Guidelines for Creating an I/O Domain

An I/O domain might have direct access to one or more I/O devices, such as PCIe buses, network interface units (NIUs), PCIe endpoint devices, and PCIe single root I/O virtualization (SR-IOV) virtual functions.

This type of direct access to I/O devices means that more I/O bandwidth is available to provide the following:

• Services to the applications in the I/O domain

• Virtual I/O services to guest domains

The following basic guidelines enable you to effectively utilize the I/O bandwidth:

• Assign CPU resources at the granularity of CPU cores. Assign one or more CPU cores based on the type of I/O device and the number of I/O devices in the I/O domain.

  For example, a 1-Gbps Ethernet device might require fewer CPU cores to utilize the full bandwidth compared to a 10-Gbps Ethernet device.

• Abide by memory requirements. Memory requirements depend on the type of I/O device that is assigned to the domain. A minimum of 4 Gbytes is recommended per I/O device. The more I/O devices you assign, the more memory you must allocate.

• When you use the PCIe SR-IOV feature, follow the same guidelines for each SR-IOV virtual function that you would use for other I/O devices. So, assign one or more CPU cores and memory (in Gbytes) to fully utilize the bandwidth that is available from the virtual function.

Note that creating and assigning a large number of virtual functions to a domain that does not have sufficient CPU and memory resources is unlikely to produce an optimal configuration.