Issue 11
© Solarflare Communications 2014
82
Solarflare Server Adapter
User Guide
TCP Segmentation Offload (TSO)
TCP Segmentation offload (TSO) offloads the splitting of outgoing TCP data into packets to the
adapter. TCP segmentation offload benefits applications using TCP. Non TCP protocol applications
will not benefit (but will not suffer) from TSO.
Enabling TCP segmentation offload will reduce CPU utilization on the transmit side of a TCP
connection, and so improve peak throughput, if the CPU is fully utilized. Since TSO has no effect on
latency, it can be enabled at all times. The driver has TSO enabled by default. Therefore, there is no
opportunity to improve performance from the default.
TSO is controlled using ethtool:
# /sbin/ethtool –K <ethX> tso <on|off>
Verification of the TSO settings may be performed by running
ethtool
with the
–k
option.
Solarflare recommend you do not disable TSO.
TCP Large Receive Offload (LRO)
TCP Large Receive Offload (LRO) is a feature whereby the adapter coalesces multiple packets
received on a TCP connection into a single call to the operating system TCP Stack. This reduces CPU
utilization, and so improves peak throughput when the CPU is fully utilized.
LRO should not be enabled if you are using the host to forward packets from one interface to
another; for example if the host is performing IP routing or acting as a layer2 bridge. The driver has
LRO enabled by default.