Online Code Layout Optimizations via OCOLOS

The processor front end has become an increasingly important bottleneck in recent years due to growing application code footprints, particularly in data centers. Profile-guided optimizations performed by compilers represent a promising approach, as they rearrange code to maximize instruction cache locality and branch prediction efficiency along a relatively small number of hot code paths. However, these optimizations require continuous profiling and rebuilding of applications to ensure that the code layout matches the collected profiles. In this article, we propose Online COde Layout OptimizationS (OCOLOS), the first online code layout optimization system for unmodified applications written in unmanaged languages. OCOLOS allows profile-guided optimization to be performed on a running process instead of being performed offline and requiring the application to be relaunched. Our experiments show that OCOLOS can accelerate MySQL by up to 41%.