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Solarflare Server Adapter User Guide
Solarflare Adapters on FreeBSD
Issue 20 © Solarflare Communications 2017 309
The FreeBSD TCP/IP stack provides a large TCP segment to the driver, which splits
the data into MSS size, each with adjusted sequence space and a hardware
calculated checksum.
Enabling TSO will reduce CPU utilization on the transmit side of a TCP connection
and 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 changed dynamically using
ifconfig
.
To enable TSO, where
sfxge<n>
is the interface name:
# ifconfig sfxge<n> tso
To disable TSO:
# ifconfig sfxge<n> ‐ tso
Verification of the TSO setting may be performed by running
ifconfig
with no
options and checking the TSO value associated with the interface. The change in TSO
can be made to persist across reboots by editing the
/etc/rc.conf
file and adding
the appropriate parameter to the single line of interface configuration data. For
example:
ifconfig_sfxge<n>="inet <IPv4 address> netmask <netmask> tso"
TCP and IP checksum offloads must be enabled for TSO to work.
NOTE: Solarflare recommend that you do not disable this setting.
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 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 LRO
is bounded by the interrupt moderation delay, and is limited if interrupt moderation
is disabled (see Interrupt Moderation (Interrupt Coalescing) on page 307 ). Enabling
LRO does not itself negatively impact latency.
The Solarflare network adapter driver enables LRO by default.
LRO is changed dynamically using
ifconfig
.
To enable LRO, where
sfxge<n>
is the interface name:
# ifconfig sfxge<n> lro
To disable LRO:
# ifconfig sfxge<n> ‐ lro
Verification of the LRO setting may be performed by running
ifconfig
with no
options and checking the LRO value associated with the interface. The change in LRO
can be made to persist across reboots by editing the
/etc/rc.conf
file and adding
the appropriate parameter to the single line of interface configuration data. For
example: