A study of the potential of locality-aware thread scheduling for GPUs

Programming models such as CUDA and OpenCL allow the programmer to specify the independence of threads, effectively removing ordering constraints. Still, parallel architectures such as the graphics processing unit (GPU) do not exploit the potential of data-locality enabled by this independence. Therefore, programmers are required to manually perform data-locality optimisations such as memory coalescing or loop tiling. This work makes a case for locality-aware thread scheduling: re-ordering threads automatically for better locality to improve the programmability of multi-threaded processors. In particular, we analyse the potential of locality-aware thread scheduling for GPUs, considering among others cache performance, memory coalescing and bank locality. This work does not present an implementation of a locality-aware thread scheduler, but rather introduces the concept and identifies the potential. We conclude that non-optimised programs have the potential to achieve good cache and memory utilisation when using a smarter thread scheduler. A case-study of a naive matrix multiplication shows for example a 87% performance increase, leading to an IPC of 457 on a 512-core GPU