2.5 Quality of Service

The CCN-502 includes end-to-end Quality of Service (QoS) capabilities that are designed to support the latency and bandwidth requirements of different types of devices.

The QoS device classes are:

Devices with bounded latency requirements

These are primarily real-time or isochronous devices that require some or all of their transactions be complete within a specific time period to meet overall system requirements. These devices are typically highly latency-tolerant within the bounds of their maximum latency requirement. Examples of this class of device include networking I/O devices and display devices.

Latency-sensitive devices

These are devices whose performance is highly impacted by the response latency incurred by their transactions. Processors are traditionally highly latency-sensitive devices, although a processor can also be a bandwidth-sensitive device depending on its workload.

Bandwidth-sensitive devices

These are devices that have a minimum bandwidth requirement to meet system requirements. An example of this class of device is a video codec engine, which requires a minimum bandwidth to sustain real-time video encode and decode throughput.

Bandwidth-hungry devices

These are devices that have significant bandwidth requirements and can use as much system bandwidth as is made available, to the limits of the system. These devices determine the overall scalability limits of a system, with the devices and system scaling until all available bandwidth is consumed.

Note:

A device might fit into more than one of these classes, depending on its requirements at any time in its workload.

Support for these different types of devices and their resulting traffic is included in the CHI architecture and in the entirety of the CCN-502 microarchitecture. Each component in the CCN-502 contributes to the overall QoS microarchitecture.

This section contains the following subsections:
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