Workload Distribution

• Load imbalance is the condition when some processors do more work then others. Load imbalance will lead to bad scalability.
• Load imbalance can be diagnosed by profiling the programs and comparing the execution times for code in different threads
• In OpenMP, compiler accepts directives for work distribution:
  • C$OMP DO SCHEDULE(type[,chunk]) where type is
    • STATIC iterations are divided into pieces at compile time (default)
    • DYNAMIC iterations assigned to processors as they finish, dynamically. This requires synchronization after each chunk iterations.
    • GUIDED pieces reduce exponentially in size with each dispatched piece
    • RUNTIME schedule determined by an environment variable OMP_SCHEDULE With RUNTIME it is illegal to specify chunk.
  • Compiler accepts -mp_schedtype=type switch

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