IBM LoadLeveler for AIX 5L: Using and Administering

network

Specifies communication protocols, adapters, and their characteristics. You need to specify this keyword when you want a task of a parallel job step to request a specific adapter that is defined in the LoadLeveler administration file. You do not need to specify this keyword when you want a task to access a shared, default adapter via TCP/IP. (A default adapter is an adapter whose name matches a machine stanza name.)

Note that you cannot specify both the network statement and the Adapter requirement (or the Adapter preference) in a job command file. Also, the value of the network keyword applies only to the job step in which you specify the keyword. (That is, this keyword in not inherited by other job steps.)

The syntax is:

network.protocol = network_type [, [usage] [, mode [, comm_level] ] ]

Where:

protocol

Specifies the communication protocol(s) that are used with an adapter, and can be the following:

MPI

Specifies the Message Passing Interface. You can specify in a job step both network.MPI and network.LAPI.

LAPI

Specifies the Low-level Application Programming Interface. You can specify in a job step both network.MPI and network.LAPI.

PVM

Specifies a Parallel Virtual Machine job. When you specify in a job step network.PVM, you cannot specify any other network statements in that job step. Also, the adapter mode must be IP.

network_type

Specifies either an adapter name or a network type. This field is required. The possible values for adapter name are the names associated with the interface cards installed on a node (for example, en0, tk1 and css0 ). If you specify a network_type you must have made sure in the admin file that the network_type identifies a unique communication path. The possible values for network type are installation-defined; the LoadLeveler administrator must specify them in the adapter stanza of the LoadLeveler administration file using the network_type keyword. For example, an installation can define a network type of "switch" to identify css0 adapters. When a switch adapter exists on a node, the network_type can be specified as csss, which indicates that striped communication should be used. For more information on:

• Specifying network type, see Step 5: Specify adapter stanzas
• Striping, see Submitting jobs that use striping

usage

Specifies whether the adapter can be shared with tasks of other job steps. Possible values are shared, which is the default, or not_shared.

mode

Specifies the communication subsystem mode used by the communication protocol that you specify, and can be either IP (Internet Protocol), which is the default, or US (User Space). Note that each instance of the US mode requested by a task running on the SP switch requires an adapter window. For example, if a task requests both the MPI and LAPI protocols such that both protocol instances require US mode, two adapter windows will be used. For more information on adapter windows, see Parallel System Support Programs for AIX Administration Guide.

comm_level

The comm_level keyword should be used to suggest the amount of inter-task communication that users expect to occur in their parallel jobs. This suggestion is used to allocate adapter device resources. For more information on device resources, consult the PSSP Admin Guide. Specifying a level that is higher than what the job actually needs will not speed up communication, but may make it harder to schedule a job (because it requires more resources). The comm_level keyword can only be specified with US mode. The three communication levels are:

LOW

Implies that minimal inter-task communication will occur.

AVERAGE

This is the default value. Unless you know the specific communication characteristics of your job, the best way to determine the comm_level is through trial-and-error.

HIGH

Implies that a great deal of inter-task communication will occur.

Example 1: To use the MPI protocol with an SP switch adapter in User Space mode without sharing the adapter, enter the following:

network.MPI = css0,not_shared,US,HIGH

Example 2: To use the MPI protocol with a shared SP switch adapter in IP mode, enter the following:

network.MPI = css0,,IP

Because a shared adapter is the default, you do not need to specify shared.

Example 3: A communication level can only be specified if User Space mode is also specified:

network.MPI = css0,,US,AVERAGE

Note that LoadLeveler can ensure that an adapter is dedicated (not shared) if you request the adapter in US mode, since any user who requests a user space adapter must do so using the network statement. However, if you request a dedicated adapter in IP mode, the adapter will only be dedicated if all other LoadLeveler users who request this adapter do so using the network statement.