A system, method, and computer program for analyzing code execution and software performance characteristics are disclosed. Samples of code during run-time or from crash logs can be displayed as both a top-down tree of calls from a particular function and a bottom-up tree of calls to the particular function. Data mining techniques, including filtering and focusing, remove code that is not of interest and display code that is more relevant to performance analysis. In particular, functions contained in libraries such as system libraries can be stripped from view. The cost associated with an excluded function can be propagated to a calling function, in either the top-down or bottom-up tree.