title: Minimum number of GPU threads to be effective
body: <p>I'm going to parallelize on CUDA a local search algorithm for some optimization problem. The problem is very hard, so the size of the practically solvable problems is quite small. 
  My concern is that the number of threads planned to run in one kernel is insufficient to obtain any speedup on GPU (even assuming all threads are coalesced, free of bank conflicts, non-branching etc.). 
  Let's say a kernel is launched for 100 threads. Is it reasonable to expect any profit from using GPU? What if the number of threads is 1000? What additional information is needed to analyze the case?</p>