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Solarflare Server Adapter User Guide
Solarflare Adapters on Linux
Issue 20 © Solarflare Communications 2017 109
• To show the current value of the per ‐ adapter LRO state:
cat /sys/class/net/ethX/device/lro
Modifying this file instantly enables or disables LRO, no reboot or driver reload is
required. This setting takes precedence over the
lro
module parameter
Current LRO settings can be identified with Linux ethtool e.g.
ethtool ‐ k ethX
TCP and IP checksum offloads must be enabled for LRO to work.
TCP Protocol Tuning
TCP Performance can also be improved by tuning kernel TCP settings. Settings
include adjusting send and receive buffer sizes, connection backlog, congestion
control, etc.
For Linux kernel versions, including 2.6.16 and later, initial buffering settings should
provide good performance. However for earlier kernel versions, and for certain
applications even on later kernels, tuning buffer settings can significantly benefit
throughput. To change buffer settings, adjust the
tcp_rmem
and
tcp_wmem
using the
sysctl
command:
• Receive buffering:
sysctl net.ipv4.tcp_rmem="<min> <default> <max>"
• Transmit buffering:
sysctl net.ipv4.tcp_wmem="<min> <default> <max>"
(
tcp_rmem
and
tcp_wmem
can also be adjusted for IPV6 and globally with the
net.ipv6 and net.core variable prefixes respectively).
Typically it is sufficient to tune just the max buffer value. It defines the largest size
the buffer can grow to. Suggested alternate values are max=500000 (1/2 Mbyte).
Factors such as link latency, packet loss and CPU cache size all influence the affect of
the max buffer size values. The minimum and default values can be left at their
defaults minimum=4096 and default=87380.
Buffer Allocation Method
The Solarflare driver has a single optimized buffer allocation strategy. This replaces
the two different methods controlled with the
rx_alloc_method
driver module
parameter which were available using 3.3 and previous drivers.
The net driver continues to expose the
rx_alloc_method
module option, but the
value is ignored and it only exists to not break existing customer configurations.