All TCP/IP tunning parameters are located under /proc/sys/net/. Here is a list of some important tuning parameters:
/proc/sys/net/core/rmem_default – Receive window size
/proc/sys/net/core/wmem_default – Send window size
/proc/sys/net/core/rmem_max – Maximum Receive Window
/proc/sys/net/core/wmem_max – Maximum Send Window
/proc/sys/net/ipv4/tcp_window_scaling – To enable larger TCP windows
Increasing the amount of memory associated with socket buffers can often improve performance. As the TCP changes its window size dynamically to compensate for network congestion, it uses an initial window size based on rmem_default and wmem_default, and the window will grow till rmem_max,wmem_max and never more than that. If you are using NFS heavily, it is recommanded to set rmem_default, rmem_max, wmem_default, wmem_max to 262143. This will increase the amount of memory available for socket input queues.
More performance related stuffs @ http://unixfoo.blogspot.com/search/label/performance