20161015 - Atomic Scatter-Only Gather-Free Machines

GPUs are build around having texture caches, and caches are build around collecting loads for the most part, because loads have the highest memory traffic typically. So if after stripping out the caches from a highly parallel machine, perhaps gathering data to centralized location for processing, and then scattering it out again, is not the best model?

One possible alternative would be to switch to a scatter-centric design. On-chip memory gets divided across all the cores. Each core contains the required remote procedure (RP) functions to interact with the data associated with the core. Programs are composed of fire-and-forget message passing. Message contains arguments to the RP and index/address of the RP to execute. The model is return-free, and the RP only has access to the arguments in the message and the local memory of the core.

This is conceptually similar to taking the GPU's global atomic without return, and making it fully programmable.

This brings up a new challenge, that in order to fully load the machine, data needs to be evenly distributed across the cores based on amount of RP access. Conceptually in this model, each core is a bank of distributed memory, and a mid-range FPGA might have upwards of 1024 banks (each one BRAM). Need to ensure an algorithm doesn't camp on one bank of memory.

Likewise if any data is duplicated across cores for the sake of higher throughput, one might want to build in something into the routing logic which takes the first found compatible core which can service the RP. Also message broadcast with variable 2D locality would be very important for data amplification.