In regards to the purpose of Async compute, there are really 2 main reasons for it:
1) It allows jobs to be cycled into the GPU during dormant phases. In can vaguely be thought of as the GPU equivalent of hyper threading. Like hyper threading, it really depends on the workload and GPU architecture for as to how important this is. In this case, it is used for performance. I can’t divulge too many details, but GCN can cycle in work from an ACE incredibly efficiently. Maxwell’s schedular has no analog just as a non hyper-threaded CPU has no analog feature to a hyper threaded one.
2) It allows jobs to be cycled in completely out of band with the rendering loop. This is potentially the more interesting case since it can allow gameplay to offload work onto the GPU as the latency of work is greatly reduced. I’m not sure of the background of Async Compute, but it’s quite possible that it is intended for use on a console as sort of a replacement for the Cell Processors on a ps3. On a console environment, you really can use them in a very similar way. This could mean that jobs could even span frames, which is useful for longer, optional computational tasks.
It didn’t look like there was a hardware defect to me on Maxwell just some unfortunate complex interaction between software scheduling trying to emmulate it which appeared to incure some heavy CPU costs. Since we were tying to use it for #1, not #2, it made little sense to bother. I don’t believe there is any specific requirement that Async Compute be required for D3D12, but perhaps I misread the spec.