Question

hey there,
assuming I have a problem where each thread calculates something (reading some parameters out of the constant memory and using them for calculation) and than stores it to a global memory matrix. this matrix gets never read, just writing access… is there now any sense of using shared memory first to store all the calculated values in and than later write them to the global memory? I think no because the writes to global memory stay the same in complete, so the writes to shared memory just add to the writes which I had before already….
Thanks!

Answer 1

There can be, depending on the access patterns in the kernel code. Using a shared memory buffer to “stage” output can be a useful way of ensure writes are coalesced, when the naive write would not be coalesced. This was pretty crucial for performance in the first couple of generations of CUDA compatible hardware (G80/G90). In newer hardware, the case for this is a lot less strong. Fermi cards have a pretty effective L1 and L2 cache scheme which can (within reason) get close to what used to be only achievable using shared memory without any extra code.

There isn’t really a general answer to this question, because it depends a lot of the specifics of what any given code does, and what target hardware it is expected to run well on.