Presentation
Are Noise-Resilient Logical Timers Useful for Performance Analysis?
DescriptionIn modern HPC systems, performance measurements are often disturbed by noise.
Because repeating measurements to increase confidence in their results is costly, alternative noise-resilient techniques are desirable.
Therefore, we implement a logical clock, which does not rely on real-time measurements, in Score-P.
We explore several methods to model computational work with the time stamps, counting OpenMP loop iterations, LLVM basic blocks/statements, or hardware counters.
We demonstrate the strengths and weaknesses of using logical time stamps in a trace analysis workflow with Score-P and Scalasca, by evaluating the performance problems we can find in three MPI+OpenMP mini-apps.
By design, logical measurements reliably show algorithmic issues, such as load imbalance, but cannot capture external aspects of program execution, for example memory contention.
In summary, logical-time based measurements are a specialized but valuable addition to the performance analyst's toolbox.
Because repeating measurements to increase confidence in their results is costly, alternative noise-resilient techniques are desirable.
Therefore, we implement a logical clock, which does not rely on real-time measurements, in Score-P.
We explore several methods to model computational work with the time stamps, counting OpenMP loop iterations, LLVM basic blocks/statements, or hardware counters.
We demonstrate the strengths and weaknesses of using logical time stamps in a trace analysis workflow with Score-P and Scalasca, by evaluating the performance problems we can find in three MPI+OpenMP mini-apps.
By design, logical measurements reliably show algorithmic issues, such as load imbalance, but cannot capture external aspects of program execution, for example memory contention.
In summary, logical-time based measurements are a specialized but valuable addition to the performance analyst's toolbox.
