TCP-Tuning

TCP Performance

This page describes how to enhance the performance of data transfers. It mainly focus on the optimization of the Linux kernel parameters.

Quattor

The Quattor TCP Tuning guide aims to be a good documentation for helping you tuning your TCP Performance with Quattor.

Kernel parameters

The following are important for TCP tuning:

• net.ipv4.tcp_rmem
• net.ipv4.tcp_wmem
• net.core.rmem_default
• net.core.wmem_default
• net.core.rmem_max
• net.core.wmem_max
• net.ipv4.tcp_dsack
• net.ipv4.tcp_sack
• net.ipv4.tcp_timestamps
• net.core.netdev_max_backlog

They can be modified with:

• Quattor ;
• YAIM ;
• Manually by modifying the /etc/sysctl.conf file.

Recommended values

• net.ipv4.tcp_rmem = 131072 1048576 2097152
• net.ipv4.tcp_wmem = 131072 1048576 2097152
• net.core.rmem_default = 1048576
• net.core.wmem_default = 1048576
• net.core.rmem_max = 2097152
• net.core.wmem_max = 2097152
• net.ipv4.tcp_dsack = 0
• net.ipv4.tcp_sack = 0
• net.ipv4.tcp_timestamps = 0
• net.core.netdev_max_backlog = 10000

External links

• http://fasterdata.es.net/
• http://monalisa.cern.ch/FDT/documentation_syssettings.html
• http://indico.cern.ch/contributionDisplay.py?sessionId=31&contribId=55&confId=61917
• http://www.psc.edu/networking/projects/tcptune/
• http://onlamp.com/pub/a/onlamp/2005/11/17/tcp_tuning.html
• http://en.wikipedia.org/wiki/TCP_tuning