SWI004 device network segmentation

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TCP Segmentation Offload (TSO) is a mechanism by which the host stack offloads certain portions of outbound TCP packet processing to the Network Interface Card (NIC) thereby reducing host CPU utilization. This functionality can significantly reduce the load on the server for certain applications which primarily transmit large amounts of data from the system. Examples include web servicing, NFS, and file transfer applications.

How It Works

The reduction in CPU utilization is achieved primarily by allowing the host to transmit large frames (frames larger than the links Maximum Transmission Unit or MTU) to the NIC which are subsequently carved up into smaller, MTU-sized frames by the NIC, before transmission on the wire. Thus instead of processing many small MTU-sized frames during transmit, the host sends fewer larger VMTU (Virtual MTU) sized frames thereby increasing the efficiency of the data transfer in the host. The VMTU is typically much larger than the links MTU; for example, on a typical Ethernet card, the link MTU is 1500 bytes while a VMTU could be as large as 64Kbytes. Greater than 50% reduction in CPU utilization has been observed on some FTP workloads.


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