| We introduce the SBT library, an on-line debugging and performance monitoring tool for shared-memory parallel programs using the single-program-multiple-data (SPMD) model of parallelism. SPMD programs often use barriers to synchronize threads of execution and to delimit the start and end of different phases of computation. Through its useful barrier constructs, dynamic performance warnings, and integration with hardware event counter libraries, SBT helps programmers localize deadlocks and performance bottlenecks in their parallel programs.; SBT is a portable library that currently supports POSLX threads and SGI Irix sproc threads, SBT also supports PAPI and Irix libperfex hardware event counter libraries. For production runs, the SBT overheads can be eliminated using conditional compilation,; In order to demonstrate SBT's applicability and usefulness, we present a performance analysis of some of the programs in the SPLASH-2 suite. The information produced by SBT is used to find bottlenecks, identify the most computationally-intensive phases, and generate graphs and tables to facilitate interpretation. In addition, we quantify the overhead incurred by the programs when they are monitored with SBT, and conclude that the cost of the instrumentation is negligible. |
