622 Adapters

Performance Report on ATM adapters 6

Tuning Guidelines

• System-related Guidelines

For the D-class servers, HP recommends the adapters be installed in the Turbo slot.

For the K-class servers, HP recommends the adapters be installed in the expansion I/O board,

avoiding the core I/O.

When installing multiple adapters, make sure the adapters are evenly distributed on the HSC IO

subsystems. This ensures efficient HSC bus utilization and better scalability. On D-class servers,

install the adapters in the Turbo slot and HSC expansion slots (where available). The T600 has

multiple HSC bus converters; so be sure the adapters are installed on different bus converters.

For best performance, the minimum memory size configuration when using a 155 Mbps adapter

is 128 Mbytes. For a 622 Mbps adapter, the minimum memory size configuration is 512 Mbytes to

get the best performance.

• Application-related Guidelines

For standard applications (for example, ftp, NFS, and others), if the socket size is configurable,

choose socket size and message length values of at least 128 Kbytes. This sets the TCP window

size parameter.

For a customized application, use SETSOCKOPT IOCTL to define a socket size of at least 128

Kbytes. When possible, design the application to use the largest message size possible.

Throughput–intensive applications can see an increase of about 20% when the application is

bound to a specific CPU. This is done as follows:

The adapter can be configured to send the interrupts to a CPU rather than sending to

multiple CPUs, which is the default. Use the alxtune tool to set the non_dist_int parameter to

“on”. This tells the adapter to send the interrupts to only one CPU. Then find out which CPU

the adapter is interrupting by using the sar command. With enough traffic on the adapter, the

sar output should show interrupts on only one CPU. The application is bound to this CPU by

using the mpctl system call.

• Network design-related Guidelines

When using LAN Emulation, HP recommends that all of the ATM systems be put on a separate

subnet and use an MTU size of 9 Kbytes for the subnet. Subnets that include legacy systems

must use an MTU size of 1516 bytes.