Cache Hierarchy
A GPU's cache hierarchy looks superficially like a CPU's — an L1 per core-analog, a shared L2 behind it — but the access pattern it's optimized for is completely different. A CPU cache is tuned for one thread's temporal and spatial locality; a GPU's L1 and L2 exist to serve tens of thousands of threads issuing memory requests in 32-wide warps, and the granularity at which those requests are actually served is the fact that explains coalescing, wasted bandwidth, and most of what looks like "mysterious" memory performance on a GPU.