RHEL5 Tuning

There are a lot of differences between Linux version 2.4 and 2.6, so first we'll cover the tuning issues that are the same in both 2.4 and 2.6. To change TCP settings in, you add the entries below to the file /etc/sysctl.conf, and then run "sysctl -p".

Like all operating systems, the default maximum Linux TCP buffer sizes are way too small. I suggest changing them to the following settings:

# increase TCP max buffer size setable using setsockopt()
net.core.rmem_max = 16777216
net.core.wmem_max = 16777216
# increase Linux autotuning TCP buffer limits
# min, default, and max number of bytes to use
# set max to at least 4MB, or higher if you use very high BDP paths
net.ipv4.tcp_rmem = 4096 87380 16777216
net.ipv4.tcp_wmem = 4096 65536 16777216
You should also verify that the following are all set to the default value of 1

sysctl net.ipv4.tcp_window_scaling
sysctl net.ipv4.tcp_timestamps
sysctl net.ipv4.tcp_sack
Note: you should leave tcp_mem alone. The defaults are fine.

You can achieve increases in bandwidth of up to 10x by doing this on some long, fast paths. This is only a good idea for Gigabit Ethernet connected hosts, and may have other side effects such as uneven sharing between multiple streams.

Also, I've been told that for some network paths, using the Linux 'tc' (traffic control) system to pace traffic out of the host can help improve total throughput.

參考網站：http://fasterdata.es.net/TCP-tuning/linux.html