Solarflare Solarflare XtremeScale series, User Manual, Page: 239 / 400

Solarflare Server Adapter User Guide
Solarflare Adapters on Windows
Issue 20 © Solarflare Communications 2017 232
TCP Checksum Offload
Checksum offload moves calculation and verification of IP Header, TCP and UDP
packet checksums to the adapter. The driver has all checksum offload features
enabled by default. Therefore, there is no opportunity to improve performance
from the default.
Checksum offload configuration is changed by changing the Offload IP Checksum,
Offload UDP Checksum and Offload TCP Checksum settings in the Network
Adapter’s Advanced Properties Page.
• To check that task offloads are enabled (e.g. checksum offload in particular),
run the following commands:
netsh interface tcp show global

netsh interface ipv4 show offload

netsh interface ipv6 show offload
• See https://msdn.microsoft.com/en ‐ us/library/windows/hardware/
ff571012%28v=vs.85%29.aspx for further relevant settings.
NOTE: Solarflare recommend you do not disable checksum offload.
Large Send Offload V2 (LSO)
Large Send Offload (LSO; also known as TCP Segmentation Offload/TSO) offloads the
splitting of outgoing TCP data into packets to the adapter. LSO benefits applications
using TCP. Applications using protocols other than TCP will not be affected by LSO.
Enabling LSO will reduce CPU utilization on the transmit side of a TCP connection
and improve peak throughput, if the CPU is fully utilized. Since LSO has no effect on
latency, it can be enabled at all times. The driver has LSO enabled by default.
Therefore, there is no opportunity to improve performance from the default.
LSO is changed by changing the Large Send Offload setting in the Network Adapter’s
Advanced Properties Page.
TCP and IP checksum offloads must be enabled for LSO to work.
NOTE: Solarflare recommend that you do not disable this setting.
Receive Segment Coalescing (RSC)
TCP Receive Segment Coalescing (RSC) is a feature whereby the adapter coalesces
multiple packets received on a TCP connection into a single larger packet before
passing this onto the network stack for receive processing. This reduces CPU
utilization and improves peak throughput when the CPU is fully utilized. The
effectiveness of RSC is bounded by the interrupt moderation delay, and is limited if
interrupt moderation is disabled (see Interrupt Moderation (Interrupt Coalescing)
on page 230 ). Enabling RSC does not itself negatively impact latency.
RSC is a Microsoft feature introduced in Windows Server 2012. RSC is enabled by
default. If a host is forwarding received packets from one interface to another then
Windows will automatically disable RSC. For more information about RSC on
Windows, see https://technet.microsoft.com/en ‐ gb/library/hh997024.aspx .