Hi @ketxxx
I went through most of the first link you posted of your RX 580 vs GTX 980 and I think it is a very good article comparing the shortcomings between the two. It's a shame that all these years later @AMD has still not done anything it seems for DirectX 11 performance.
I took some screenshots of Deus Ex Mankind Divided in 720p high as well to demonstrate the DX11 performance, even more disturbing is the DX12 performance, and as you said it seem they simply wrapped DX11 to DX12 just to get improved MultiGPU support.
RX 480:
GTX 1060 3GB:
Even tried forcing max CPU load by setting my FX 8350 to 2modules 4ALUs and it proved my guess of the Nvidia driver wrong:
RX 480:
GTX 1060:
Kind regards
As for CPU exacerbating the AMD DX11 Problem.
Before Zen 3, AMD had really poor core-to-core latency. This can exacerbate the issue when faced with frequent context switching. Imagine that on the thread where draw calls are computed, there are also other compute heavy tasks. Since draw calls are computed on single thread in AMD driver, the driver[depending also on game engine] can switch the context from clogged thread to other less congested thread. But this comes with latency penalty. The switching can occur several times, before computation is complete. This is why AMD gpus had less "loading" stutter on intel cpus at the time in DX11 cpu heavy scenarios. The problem would not be so severe if the draw call pipeline was always offloaded to the nearest thread like from thread 0 to thread 1, but it's not always the case if thread 1 is also pegged.
As you can see in Zen 2 switching between cores incurs 30ns of latency, with 7ns of latency if its between the same core but virtual thread[hyperthreading]. In contrast switching between CCX incurs massive latency and should be always avoided in critical computation pipeline like draw calls.
Zen 3 improved the situation
And here's intel cpus[along ryzen too].
Intel has comparable inter core latencies, slightly lower than ZEN2, slightly higher than ZEN3, BUT the latencies are EVEN!. There's no problem between switching CCX and added huge latency malus. This is why when you compare ZEN 2 vs intel 9/10/11 series in AIDA latency benchmark you will see two times less latency for intel. Imagine that a game do this context switching between CCX like you usually will have with CPUs that have less than 8 logical cores for example -ZEN 2 Ryzen 5 under heavy CPU scenario with a draw call computation on single thread like with AMD DX11 driver. It's a disaster, hence AMD CPU exacerbate the issue of their poor drivers. This was VASTLY improved with ZEN+/ZEN2, compared to ZEN/bulldozer. Bulldozer and even ZEN was a complete disaster, hence poor performance in heavy cpu scenarios and unbearable stutter. Anyone who bought AMD CPU back then was completely duped few years later when multithreading became more common even with DX11, and AMD refused to improve their drivers. They were and still are in hot water, hence they pushed SO HARD Mantle, Vulkan and DX12. Back at bulldozer era even BIGGEST AMD fanboys admitted that it's better to run intel cpu and amd gpu. But the obvious solution back then and still today is ALWAYS to buy Intel and Nvidia, until AMD will clearly improve. This is especially true if you like to play DX11 games[especially high refresh rate] or oldies in DX9.
