Defensive loop tiling for shared cache

Loop tiling is a compiler transformation that tailors an application´s working set to fit in a cache hierarchy. On today´s multicore processors, part of the hierarchy especially the last level cache (LLC) is shared. The available cache space in shared cache changes depending on co-run applications. Furthermore on machines with an inclusive cache hierarchy, the interference in the shared cache can cause evictions in the private cache, a problem known as the inclusion victims. This paper presents defensive tiling, a set of compiler techniques to estimate the effect of cache sharing and then choose the tile sizes that can provide robust performance in co-run environments. The goal of the transformation is to optimize the use of the cache while at the same time guarding against interference. It is entirely a static technique and does not require program profiling. The paper shows how it can be integrated into a production-quality compiler and evalutes its effect on a set of tililing benchmarks for both program co-run and solo-run performance, using both simulation and testing on real systems.