IBM Power Systems 775 Manual

Contents

Chapter 1. Understanding the IBM Power Systems 775 Cluster 91MPI and LAPI provide communication between parallel tasks, enabling application programsto be parallelized.MPI provides message passing capabilities that enable parallel tasks to communicate dataand coordinate execution. The message passing routines call communication subsystemlibrary routines to handle communication among the processor nodes.LAPI differs from MPI in that LAPI is based on an active message style mechanism thatprovides a one-sided communications model in which one process initiates an operation. Thecompletion of that operation does not require any other process to take a complementaryaction. LAPI also is the common transport layer for MPI and is packaged as part of the AIXRSCT component.Parallel Environment debug environmentThe parallel debugger (pdb) streamlines debugging of parallel applications, presenting theuser with a single command line interface that supports most dbx/gdb execution controlcommands and the ability to examine running tasks. To simplify the management of a largenumbers of tasks, dbx/gdb grpups tasks together so that the user might examine any subsetof the debugged tasks.PDB allows users to invoke a POE job or attach to a running POE job and place it underdebug control. pdb starts a remote dbx/gdb session for each task of the POE job that isplaced under debugger control.PDB provides advanced features, including: dynamic tasking support, multiple consoledisplay, and output filtering.Active Messaging Interface: Beginning with Parallel Environment Runtime Editionversion 1.1 for AIX, the low-level application programming interface (LAPI) was replaced bya new messaging API called the parallel active messaging interface (PAMI). LAPIsupported only point-to-point communications and PAMI supports both point-to-point andcollective communications.This change means that PE MPI now runs on top of PAMI. Existing calls to LAPIpoint-to-point functions are replaced by PAMI point-to-point functions, and some collectivesare replaced by PAMI collectives.LAPI is still supported by PE. However, because LAPI no longer receives any functionalenhancements, and PE removes support for LAPI, users must migrate from LAPI to PAMI.For more information about installing LAPI or PAMI, see Parallel Environment RuntimeEdition for AIX V1.1: Installation, SC23-6780. For more information about migrating fromLAPI to PAMI, and about PAMI in general, see the IBM Parallel Environment RuntimeEdition: PAMI Programming Guide, SA23-2273.