I am going to buy a ASRock x370 killer SLI/ac motherboard. I am also buying two AMD Radeon Vega 64 GPUs. Using OpenCL or OpenGL, can I transfer some data from the RAM into two GPUs parallely at the same time?
Will the speed become twice the speed of transferring data into one GPU?
I don't know if you can do two simultaneous DMA transfers. Your best bet would be to benchmark this. Create a small program that has two threads and attempts to DMA to the two cards at once. Record the high precision times of the start and finish to see if they actually occur in parallel.
But with two graphics cards, the PCIe bandwidth is 1/2 what it is if you have a single card. Each transfer would be 1/2 the speed if you had a single card.