Tuning operating systems and network settings

Network tuning can reduce Transmission Control Protocol (TCP) stack delay by changing connection settings and can improve throughput by changing TCP buffers.

Operating systems

The tuning settings might improve WebSphere® eXtreme Scale performance. Tune according to your network and application load.

Windows:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\
Tcpip\Parameters
MaxFreeTcbs = dword:00011940
MaxHashTableSize = dword:00010000
MaxUserPort = dword:0000fffe
TcpTimedWaitDelay = dword:0000001e

Solaris:

ndd -set /dev/tcp tcp_time_wait_interval 60000
fndd -set /dev/tcp tcp_keepalive_interval 15000
ndd -set /dev/tcp tcp_fin_wait_2_flush_interval 67500
ndd -set /dev/tcp tcp_conn_req_max_q 16384
ndd -set /dev/tcp tcp_conn_req_max_q0 16384
ndd -set /dev/tcp tcp_xmit_hiwat 400000
ndd -set /dev/tcp tcp_recv_hiwat 400000
ndd -set /dev/tcp tcp_cwnd_max 2097152
ndd -set /dev/tcp tcp_ip_abort_interval 20000
ndd -set /dev/tcp tcp_rexmit_interval_initial 4000
ndd -set /dev/tcp tcp_rexmit_interval_max 10000
ndd -set /dev/tcp tcp_rexmit_interval_min 3000
ndd -set /dev/tcp tcp_max_buf 4194304

AIX®:

/usr/sbin/no -o tcp_sendspace=65536
/usr/sbin/no -o tcp_recvspace=65536
/usr/sbin/no -o udp_sendspace=65536
/usr/sbin/no -o udp_recvspace=65536
/usr/sbin/no -o somaxconn=10000
/usr/sbin/no -o tcp_nodelayack=1
/usr/sbin/no –o tcp_keepinit=40
/usr/sbin/no –o tcp_keepintvl=10

Linux:

sysctl -w net.ipv4.tcp_timestamps=0 
sysctl -w net.ipv4.tcp_tw_reuse=1 
sysctl -w net.ipv4.tcp_tw_recycle=1 
sysctl -w net.ipv4.tcp_fin_timeout=30 
sysctl -w net.ipv4.tcp_keepalive_time=1800 
sysctl -w net.ipv4.tcp_rmem="4096 87380 8388608" 
sysctl -w net.ipv4.tcp_wmem="4096 87380 8388608" 
sysctl -w net.ipv4.tcp_max_syn_backlog=4096

HP-UX:

ndd -set /dev/tcp tcp_ip_abort_cinterval 20000

Jumbo frames

For Ethernet networks, enabling jumbo frames (frame size or Maximum Transmission Unit (MTU) of 9000 bytes) on all systems (hosts and switches) can provide a significant performance improvement, especially when the application uses large payload sizes. Check the operating instructions for the particular host and switches in your network for information about how to enable jumbo frames. The steps to configure jumbo frames are particular to each equipment type.

Note: Enabling jumbo frames on some hosts in the configuration and not others can cause the switch to become a bottleneck point. The switch must convert between frame sizes on different ports. Therefore, it is best to enable jumbo frames on all hosts in the configuration or none of the hosts in the configuration.