TCP-capable Network Fabrics Control

I_MPI_TCP_NETMASK

(I_MPI_NETMASK)

Choose the network interface for MPI communication over TCP-capable network fabrics.

Syntax

I_MPI_TCP_NETMASK=<arg>

Arguments

<arg>

Define the network interface (string parameter)

<interface_mnemonic>

Mnemonic of the network interface: ib or eth

ib

Use IPoIB* network interface

eth

Use Ethernet network interface. This is the default value

<interface_name>

Name of the network interface

Usually the UNIX* driver name followed by the unit number

<network_address>

Network address. Trailing zero bits imply a netmask

<network_address/

<netmask>

Network address. The <netmask> value specifies the netmask length

<list of interfaces>

A colon separated list of network addresses and interface names

Description

Set this environment variable to choose the network interface for MPI communication over TCP-capable network fabrics. If you specify a list of interfaces, the first available interface on the node is used for communication.

Examples

I_MPI_TCP_BUFFER_SIZE

Change the size of the TCP socket buffers.

Syntax

I_MPI_TCP_BUFFER_SIZE=<nbytes>

Arguments

<nbytes>

Define the size of the TCP socket buffers

> 0

The default <nbytes> value is equal to default value of the TCP socket buffer size on your Linux system.

Description

Set this environment variable to manually define the size of the TCP socket buffers. The TCP socket buffer size is restricted by the existing TCP settings on your Linux system.

Use the I_MPI_TCP_BUFFER_SIZE environment variable for tuning your application performance for a given number of processes.

Note

TCP socket buffers of a large size can require more memory for an application with large number of processes. Alternatively, TCP socket buffers of a small size can considerably decrease the bandwidth of each socket connection especially for 10 Gigabit Ethernet and IPoIB (see I_MPI_TCP_NETMASK for details).

I_MPI_TCP_POLLING_MODE

Set this environment variable to define a polling mode.

Syntax

I_MPI_TCP_POLLING_MODE=<mode>

Arguments

<mode>

Specify the polling mode

poll

The polling mode based on the poll() function. This is the default value

epoll[:edge]

The polling mode based on the epoll() function as an edge-triggered interface

epoll:level

The polling mode based on the epoll() function as a level-triggered interface

Set this environment variable to select the polling mode for the tcp fabric.

Use the I_MPI_TCP_POLLING_MODE environment variable for tuning application performance. You can choose the best polling mode on an experimental basis. The best mode depends on the specific application and on the number of processes. The epoll polling mode is a preferable mode in the following situations: