Contention tracking in GPU last-level cache

Abstract

The Last-level cache (LLC) is one of the main GPU’s shared resources that contributes to improve performance but also increases individual kernel’s performance variability. This is detrimental in scenarios in which some level of performance predictability is required. While predictability can be regained by deploying cache partitioning (isolation) mechanisms, isolation negatively affects performance efficiency. This work shows that not partitioning the LLC and providing the ability to track the contention that kernels generate on each other allows them to share LLC space, hence increasing efficiency, while the system designer obtains a clear view of how each kernel affects each other in the LLC so as to balance performance and predictability goals. In this line, we propose GPU demotion counters (GDC), a low-overhead hardware mechanism to track contention that kernels generate on each other in the shared LLC.