HP-UX TCP/IP Performance White Paper, March 2008

Sockets Tunables

socket_buf_max:

Specifies the maximum socket buffer size for AF_UNIX sockets.

[1024,2147483647] Default: 262144 bytes

socket_caching_tcp:

Enables or disables socket caching for TCP sockets for

AF_INET and AF_INET6 address families. This value determines

how many data structures for TCP sockets the system caches

per CPU for each address family. Enabling this feature can

improve system performance considerably if the system uses

many short-lived connections.

The value of 0 (zero) disables the feature. The value of 1

enables the feature and sets the cache size to 512 entries

per address family per CPU, which is also the default value.

Any value greater than 1 sets the cache size to the specified

value. [0-2147483647] Default: 512 (caching)

The HP-UX 11i transport builds a "stream" for each connection. On that "stream" are placed STREAMS

modules for a stream-head, TCP and IP as well as socket data structures (when BSD/XOPEN sockets are in

use). These structures can be cached to accelerate connection establishment.

HP-UX 11i v1 and 11i v2 support caching of IPv4 TCP connection only. HP-UX 11i v3 has been enhanced

such that both IPv4 and IPv6 TCP connections are cached.

For virtually all situations, the default value of 512 is sufficient.

Refer to section 4.2.2 for the detailed discussion of “Socket caching for TCP connections".

socket_enable_tops:

Controls the IP optimization feature named TOPS (Thread-Optimized

Packet Scheduling.

Modifying TOPS can result in improved scalability of TCP and UDP

socket applications on multiprocessor systems.

[0-2] Default: 1 (TOPS Mode 1) for 11i v1 and 11i v2

Default: 2 (TOPS Mode 2) for 11i v3

The behavior depends on what value socket_enable_tops is set to:

0: Disables the TOPS feature.

1: Enables the TOPS feature in Mode 1.

This parameter setting can help improve systems using a mix of

short and long-lived TCP socket connections.

2: Enables the TOPS feature in Mode 2.

This parameter setting is the default value for 11i v3 and is

optimal for most system configurations as well as systems using

infrequent long-lived connections.

Refer to section 3.1 for the detailed discussion of TOPS.