How To: Network / TCP / UDP Tuning
This is a very basic step by step description of how to improve the performance
networking (TCP & UDP) on Linux 2.4+ for high-bandwidth applications. These settings are especially
important for GigE links. Jump to Quick Step or
All The Steps.
This howto assumes that the machine being tuned is involved in supporting high-bandwidth
applications. Making these modifications on a machine that supports multiple users and/or
multiple connections is not recommended - it may cause the machine to deny connections
because of a lack of memory allocation.
Cut and paste the following into a linux shell with root privleges:
- Make sure that you have root privleges.
- Type: sysctl -p | grep mem
This will display your current buffer settings. Save These! You may want to
roll-back these changes
- Type: sysctl -w net.core.rmem_max=8388608
This sets the max OS receive buffer size for all types of connections.
- Type: sysctl -w net.core.wmem_max=8388608
This sets the max OS send buffer size for all types of connections.
- Type: sysctl -w net.core.rmem_default=65536
This sets the default OS receive buffer size for all types of connections.
- Type: sysctl -w net.core.wmem_default=65536
This sets the default OS send buffer size for all types of connections.
- Type: sysctl -w net.ipv4.tcp_mem='8388608 8388608 8388608'
TCP Autotuning setting. "The tcp_mem variable defines how the TCP stack should behave when it comes to memory usage. ...
The first value specified in the tcp_mem variable tells the kernel the low threshold. Below this
point, the TCP stack do not bother at all about putting any pressure on the memory usage by
different TCP sockets. ... The second value tells the kernel at which point to start pressuring
memory usage down. ... The final value tells the kernel how many memory pages it may use maximally.
If this value is reached, TCP streams and packets start getting dropped until we reach a lower memory
usage again. This value includes all TCP sockets currently in use."
- Type: sysctl -w net.ipv4.tcp_rmem='4096 87380 8388608'
TCP Autotuning setting. "The first value tells the kernel the minimum receive buffer for each TCP connection,
and this buffer is always allocated to a TCP socket, even under high pressure on the system. ...
The second value specified tells the kernel the default receive buffer allocated for each TCP
socket. This value overrides the /proc/sys/net/core/rmem_default value used by other protocols. ...
The third and last value specified in this variable specifies the maximum receive buffer that can
be allocated for a TCP socket."
- Type: sysctl -w net.ipv4.tcp_wmem='4096 65536 8388608'
TCP Autotuning setting. "This variable takes 3 different values which holds information on how much
TCP sendbuffer memory space each TCP socket has to use. Every TCP socket has this much buffer space to
use before the buffer is filled up. Each of the three values are used under different conditions. ...
The first value in this variable tells the minimum TCP send buffer space available for a single TCP socket. ...
The second value in the variable tells us the default buffer space allowed for a single TCP socket to use. ...
The third value tells the kernel the maximum TCP send buffer space."
- Type:sysctl -w net.ipv4.route.flush=1
This will enusre that immediatly subsequent connections use these values.
sysctl -w net.core.rmem_max=8388608
sysctl -w net.core.wmem_max=8388608
sysctl -w net.core.rmem_default=65536
sysctl -w net.core.wmem_default=65536
sysctl -w net.ipv4.tcp_rmem='4096 87380 8388608'
sysctl -w net.ipv4.tcp_wmem='4096 65536 8388608'
sysctl -w net.ipv4.tcp_mem='8388608 8388608 8388608'
sysctl -w net.ipv4.route.flush=1
All of this information comes directly from these very reliable sources:
Please send me some
on how this worked for you. I'd be happy to help you figure it out on yours.
I've used these or similar settings for a number of high-bandwidth applications with great results.