Originally Posted by Mahigan Warning: Spoiler! (Click to show)
Now we know that the a PCIe 2.0 x8 slot (8 GB/s) bottlenecks an AMD R9 290 under Ashes of the Singularity.
I don't think it is CPU related.
PontiacGTX shared this link with me and I believe he is onto something: http://www.hardwaresecrets.com/everything-you-need-to-know-about-the-hypertransport-bus/4/
Now granted the AMD 990FX uses a 3200MHz HT 3.1 link which results in 6,400 MT/s or 12,800 MB/s now look at the schematic below:
The AMD FX Processor communicates with the 990FX Northbridge at 12.8GB/s which talks to the PCIe 2.0 ports at 16GB/s. Therefore, for all intents and purposes, the AMD FX Processor talks to the Graphics card at 12.8GB/s, even if the Graphics card is running on a PCIe 2.0 x16 port.
Therefore the culprit for poor AMD performance could very well be the Hypertransport Link.
Take Battlefield 4, it's a DX11 title that is heavy on draw calls (for a DX11 game):
PCIe 2.0 x8 is saturated already (8 GB/s).
Warning: Spoiler! (Click to show)
Now imagine having all those CPU cores, now available in DX12, making draw calls ontop of the textures etc travelling over the bus? For an AMD system, this is further compounded by the slow HT 3.1 link (12.8GB/s) and that's in the best case scenario (990/FX chipset). If you're using a 970 chipset, you're knocked down to HT 3.0 or 10.4 GB/s. The 3D Mark Overhead API test isn't sending textures either (or any other heavy command), it's only sending draw calls. So it really wouldn't show up on that test.
Again... just a theory.
Can you please elucidate the part about 290 with direct pointers? I cannot distinguish whether there has been a prior 290 example that I missed, or gtx 980 implies the a similar phenomenon.