Issue 11
© Solarflare Communications 2014
81
Solarflare Server Adapter
User Guide
To set TX interrupt moderation, if
separate_tx_channels
is enabled:
ethtool –C <ethX> tx-usecs 0 tx-frames 0
or
ethtool –C <ethX> tx-usecs 0 tx-frames 1
Interrupt moderation settings can be checked using
ethtool
–c
.
The interrupt moderation interval is critical for tuning adapter latency:
• Increasing the moderation value will increase latency, but reduce CPU utilization and improve
peak throughput, if the CPU is fully utilized.
• Decreasing the moderation value or turning it off will decrease latency at the expense of CPU
utilization and peak throughput.
For many transaction request-response type network applications, the benefit of reduced latency to
overall application performance can be considerable. Such benefits may outweigh the cost of
increased CPU utilization.
TCP/IP Checksum Offload
Checksum offload moves calculation and verification of IP Header, TCP and UDP packet checksums
to the adapter. The driver by default has all checksum offload features enabled. Therefore, there is
no opportunity to improve performance from the default.
Checksum offload is controlled using ethtool:
Receive Checksum:
# /sbin/ethtool –K <ethX> rx <on|off>
Transmit Checksum:
# /sbin/ethtool –K <ethX> tx <on|off>
Verification of the checksum settings may be performed by running ethtool with the
–k
option.
Solarflare recommend you do not disable checksum offload.
NOTE:
The interrupt moderation interval dictates the minimum gap between two consecutive
interrupts. It does not mandate a delay on the triggering of an interrupt on the reception of every
packet. For example, an interrupt moderation setting of 30
μ
s will not delay the reception of the
first packet received, but the interrupt for any following packets will be delayed until 30
μ
s after the
reception of that first packet.