Performance Accountability for Optimizing Compilers

The Faculty of Informatics is pleased to announce a seminar given by Tipp Moseley

TITLE: Performance Accountability for Optimizing Compilers
SPEAKER: Tipp Moseley, post-doctoral researcher, Université de Versailles
DATE: Thursday August 27th, 2009
PLACE: USI Università della Svizzera italiana, room SI-006, Informatics building (Via G. Buffi 13)
TIME: 10.30

ABSTRACT:
Compilers employ many aggressive code transformations to achieve highly optimized code.  However, because of complex target architectures and unpredictable optimization interactions, these transformations may not always be beneficial.  Advances in hardware ensure that instruction set architectures are undergoing continual evolution.  As a result, compilers are under constant pressure to adapt and take full advantage of available features.

Current techniques for evaluating code generation only compare profiles at the application level, but a fundamental step in tuning compiler performance is identifying the specific examples that can be improved.  Quantitative function- and loop-level comparisons were previously not possible because techniques did not exist to compare them coherently after optimizations have been applied.  To ensure the best performance is achieved, a more rigorous approach is necessary.

This work presents two toolchain-independent techniques to better measure and understand relative profile differences across binary programs (produced from the same source) compiled with different compilers, optimizations, or target architectures.  OptiScope uses aggregate profile counts to match analogous code regions in different binaries.  OptiScope has low overhead, but it only works on programs with identical inter-procedural optimizations applied.  For programs with arbitrary transformations applied, including inter-procedural optimization, the Chainsaw tool uses more heavyweight analysis on execution logs to match semantically identical intervals of execution. To support each of these applications, I present novel techniques for low-overhead profile collection and seekable event log compression. Both binary matching  approaches generate thousands of comparable regions from only a small set of benchmarks, and hundreds of key performance metrics for each region are loaded into a relational database to enable rapid querying for outliers.  Case studies show the tools are proficient in identifying performance differences from 32.5% to 893% on select regions of SPEC 2006 benchmarks.

BIO:
Tipp Moseley recently received his Ph.D. from the University of Colorado and is currently a post-doctoral researcher at the Universite de Versailles.  He will be joining Google in Mountain View, California full time in October.  His research interests include profiling, performance analysis, and compilers.  Relevent publications are available at http://systems.cs.colorado.edu/~moseleyt/publications

HOST: Prof. Matthias Hauswirth