Introduction - Chelsio Communications Terminator Series Installation And User Manual

Chapter XVII. UDP Segmentation Offload and Pacing

Introduction

Chelsio's Terminator series of adapters provide UDP segmentation offload and per-stream rate
shaping to drastically lower server CPU utilization, increase content delivery capacity, and
improve service quality.
Tailored for UDP content, UDP Segmentation Offload (USO) technology moves the processing
required to packetize UDP data and rate control its transmission from software running on the
host to the network adapter. USO increases performance and dramatically reduces CPU
overhead, allowing significantly higher capacity using the same server hardware. Without USO
support, UDP server software running on the host needs to packetize payload into frames,
process each frame individually through the network stack and schedule individual frame
transmission, resulting in millions of system calls, and packet traversals through all protocol layers
in the operating system to the network device. In contrast, USO implements the network protocol
stack in the adapter, and the host server software simply hands off unprocessed UDP payload in
large I/O buffers to the adapter.
The following figure compares the traditional datapath on the left to the USO datapath on the
right, showing how per-frame processing is eliminated. In this example, the video server pushes
5 frames at a time. In an actual implementation, a video server pushes 50 frames or more in each
I/O, drastically lowering the CPU cycles required to deliver the content.
Pacing is beneficial for several reasons, one example is for Content Delivery Networks
(CDNs)/Video On Demand (VOD) providers to avoid receive buffer overflows, smooth out network
traffic, or to enforce Service Level Agreements (SLAs).
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