Does FetchSize and WriteSize work for OpenGL? It seems they are only enabled for OpenCL in GPUPerfAPI. Are there any other ways to measure OpenGL video memory bandwidth?
You can calculate video memory bandwidth by multiplying the memory speed by bus width. For example a R9 380 (256-bit memory bus) with a 1.5Ghz (6Gbps) memory clock has a bandwidth of 256/8 * 6 = 192GB/s peak memory bandwidth. Note that you must read at least 2 cache lines per page to achieve the full memory bandwidth. 64-byte random reads would be limited to half the peak bandwidth.