Oct 082008

openSUSE and SUSE Linux sets default values for some of the network related Kernel parameters. While these are certainly not something that reduces the performance on your linux but are set considering optimal across platforms. With Kernel 2.6 (default in recent releases of openSUSE & SuSE Linux), there are some fine tuning you can do to improve Network performance and get that extra out of your system.

The parameters that we focus to improve performance are


Sets the Maximum Socket Receive Buffer for all protocols


sets the Maximum Socket Send Buffer for all protocols


Sets the Maximum Socket Receive Buffer for TCP Protocol (overides the defaults set by net.core.rmem_default)


Sets the Maximum Socket Send Buffer for TCP Protocol (overides the defaults set by net.core.wmem_default)


Enables/Disables the behaviour of cachek performance charecteristics connection. By default, Linux Kernel remembers connection performance and congestion charecteristics.


Sometimes, packet reordering in a network can be interpreted as packet loss and hence increasing the value of this parameter should improve performance (default is “3”)


You can set this to one of the manu available high speed congestion variants like “cubic” “hs-tcp” (default is “reno”)

Before we set the values, lets look at the current values.

The following displays a long list of current values set for the Kernel Paramters.

opensuse11:~ # sysctl -a

To view the values of interest here

opensuse11:~ # sysctl -a | egrep “rmem|wmem|tcp_congestion|reordering|metrics”| egrep -v “default|udp|lowmem”
net.ipv4.tcp_reordering = 3
net.ipv4.tcp_wmem = 4096        16384   4194304
net.ipv4.tcp_rmem = 4096        87380   4194304
net.ipv4.tcp_no_metrics_save = 0
net.ipv4.tcp_congestion_control = reno
net.core.wmem_max = 131071
net.core.rmem_max = 131071

We can set the values are as follows:

net.ipv4.tcp_reordering = 20
net.ipv4.tcp_wmem = 8192 87380 16777216
net.ipv4.tcp_rmem = 8192 87380 16777216
net.ipv4.tcp_no_metrics_save = 1
net.ipv4.tcp_congestion_control = cubic
net.core.wmem_max = 16777216
net.core.rmem_max = 16777216

To set the values to be set at boot time, we need to edit the file “/etc/sysctl.conf” and add the above lines. However, this will not take effect immediatly. To make the changes to take effect immediatly,

opensuse11:~ # sysctl -p /etc/sysctl.conf

Alternatively, you can set one parameter value at a time as follows:

opensuse11:~ # sysctl -w net.ipv4.tcp_reordering=20

opensuse11:~ # sysctl -w net.ipv4.tcp_wmem=”8192 87380 16777216″

opensuse11:~ # sysctl -w net.ipv4.tcp_rmem=”8192 87380 16777216″

opensuse11:~ # sysctl -w net.ipv4.tcp_no_metrics_save=1

opensuse11:~ # sysctl -w net.ipv4.tcp_congestion_control=cubic

opensuse11:~ # sysctl -w net.core.wmem_max=16777216

This should improve Network Performance on your SuSE or openSUSE Linux.