Folding: Detailed analysis with coarse sampling

Abstract

Performance analysis tools help the application users to find bottlenecks that prevent the application to run at full speed in current supercomputers. The level of detail and the accuracy of the performance tools are crucial to completely depict the nature of the bottlenecks. The details exposed do not only depend on the nature of the tools (profile-based or trace-based) but also on the mechanism on which they rely (instrumentation or sampling) to gather information. In this paper we present a mechanism called folding that combines both instrumentation and sampling for trace-based performance analysis tools. The folding mechanism takes advantage of long execution runs and low frequency sampling to finely detail the evolution of the user code with minimal overhead on the application. The reports provided by the folding mechanism are extremely useful to understand the behavior of a region of code at a very low level.We also present a practical study we have done in a in-production scenario with the folding mechanism and show that the results of the folding resembles to high frequency sampling. © Springer-Verlag Berlin Heidelberg 2012.