Exploiting hardware performance counters with flow and context sensitive profiling

Abstract

A program profile attributes run-time costs to portions of a program's execution. Most profiling systems suffer from two major deficiencies: first, they only apportion simple metrics, such as execution frequency or elapsed time to static, syntactic units, such as procedures or statements; second, they aggressively reduce the volume of information collected and reported, although aggregation can hide striking differences in program behavior. This paper addresses both concerns by exploiting the hardware counters available in most modern processors and by incorporating two concepts from data flow analysis-flow and context sensitivity-to report more context for measurements. This paper extends our previous work on efficient path profiling to flow sensitive profiling, which associates hardware performance metrics with a path through a procedure. In addition, it describes a data structure, the calling context tree, that efficiently captures calling contexts for procedure-level measurements. Our measurements show that the SPEC95 benchmarks execute a small number (3-28) of hot paths that account for 9-98% of their L1 data cache misses. Moreover, these hot paths are concentrated in a few routines, which have complex dynamic behavior.