Solarflare Solarflare XtremeScale series, User Manual, Page: 113 / 400

Solarflare Server Adapter User Guide
Solarflare Adapters on Linux
Issue 20 © Solarflare Communications 2017 106
For many transaction request ‐ response type network applications, the benefit of
reduced latency to overall application performance can be considerable. Such
benefits typically outweigh the cost of increased CPU utilization. It is recommended
that:
• Interrupt moderation is disabled for applications that require best latency and
jitter performance, such as market data handling.
• Interrupt moderation is enabled for high throughput single (or few) connection
TCP streaming applications, such as iSCSI.
Interrupt moderation can be changed using ethtool, where
ethX
is the interface
name. Before adjusting the interrupt moderation interval, it is recommended to
disable adaptive moderation:
ethtool ‐ C <ethX> adaptive ‐ rx off
To set the RX interrupt moderation
interval
in microseconds ( μ s):
ethtool –C <ethX> rx ‐ usecs <interval>
To turn off interrupt moderation, set an interval of zero (0):
ethtool –C <ethX> rx ‐ usecs 0
The above example also sets the transmit interrupt moderation interval, unless the
driver module parameter
separate_tx_channels
is enabled. (Normally packet RX
and TX completions will share interrupts, so RX and TX interrupt moderation
intervals must be equal, and the adapter driver automatically adjusts tx ‐ usecs to
match rx ‐ usecs.) Refer to Table 27 on page 123 .
To set the TX interrupt moderation interval, if
separate_tx_channels
is enabled:
ethtool –C <ethX> tx ‐ usecs <interval>
Interrupt moderation settings can be checked using
ethtool –c
.
NOTE: The performance benefits of TCP Large Receive Offload are limited if
interrupt moderation is disabled. See TCP Large Receive Offload (LRO) on page 107 .
TCP/IP 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 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.
NOTE: Solarflare recommend you do not disable checksum offload.