wow, 226 gb/s. wonder if stuff is really being copied.
yeahhh, if we multiply the stream data by 0.5, we get 0.38 gb/s.
removed some copies to host (writing images from other functions) ... now seeing 4.6 GB/s stream
even with cudaDeviceSynchronize before the timers, it looks like previous copies back to host are affecting runtime of stream benchmark