You can use TCP segmentation offload support to have the TCP/IP
stack offload most IPv4 and IPv6 outbound TCP segmentation processing
in QDIO mode to an OSA-Express feature. You can configure this function
by specifying the SEGMENTATIONOFFLOAD parameter on the IPCONFIG or
IPCONFIG6 profile statement. You must also offload checksum processing
to the OSA-Express feature to enable segmentation offload. The TCP/IP
stack performs TCP segmentation processing in the following cases
in which segmentation cannot be offloaded:
- IPv6 packets sent to and from OSA-Express features that support
only IPv4 segmentation offload (OSA-Express3 and earlier features)
- Packets that go directly to another stack that shares the same
OSA-Express port
- IPSec-encapsulated packets
- When multipath is in effect (unless all interfaces in the multipath
group support segmentation offload)
- When the SEGMENTATIONOFFLOAD parameter is not specified on the
IPCONFIG or IPCONFIG6 statement
Tip: Applications that use large TCP send buffers will
obtain the most benefit from TCP segmentation offload. The size of
the TCP receive buffer on the other side of the TCP connection also
affects the negotiated buffer size. You can control the size of these
buffers using the following mechanisms:
- The TCPSENDBFRSIZE parameter on the TCPCONFIG statement sets the
default TCP send buffer size for all applications.
- An application can use the SO_SNDBUF socket option to override
the default TCP send buffer size.
- The TCPRCVBUFRSIZE parameter on the TCPCONFIG statement sets the
default TCP receive buffer size for all applications.
- An application can use the SO_RCVBUF socket option to override
the default TCP receive buffer size.
Requirement: To determine the OSA microcode
level required to use TCP segmentation offload support, see the Preventive
Service Planning (PSP) bucket for the appropriate device.