Also a fast read/write on chip memory scratchpad (or a big cache) would help a lot with image post processing. Most of the image post process algorithms need no (or just a little) extra memory in addition to the processed backbuffer. With large enough on chip memory (or cache), most post processing algorithms become completely free of external memory bandwidth. Examples: HDR bloom, lens flares/streaks, bokeh/DOF, motion blur (per pixel motion vectors), SSAO/SSDO, post AA filters, color correction, etc, etc. The screen space local reflection (SSLR) algorithm (in Killzone Shadow Fall) would benefit the most from fast on chip local memory, since tracing those secondary rays from the min/max quadtree acceleration structure has quite an incoherent memory access pattern. Incoherent accesses are latency sensitive (lots of cache misses) and the on chip memories tend to have smaller latencies (of course it's implementation specific, but that is usually true, since the memory is closer to the execution units, for example Haswell's 128 MB L4 should be lower latency than the external memory). I would expect to see a lot more post process effects in the future as developers are targeting cinematic rendering with their new engines. Fast on chip memory scratchpad (or a big cache) would reduce bandwidth requirement a lot.
