Does the LRLink PCIe Bridge Fix RCCL's Broken P2P on Dual R9700? (Update: Yes it does!)

Prom21 Sidebar

(this might deserve its own topic, or it might have already been talked about elsewhere but I couldn’t find it)

If anyone out there was hoping the prom21 chipset pcie card from wisdipi would function in a similar manner to the lrlink but at a lower link speed and width, it does not seem to. It appears to have a much more complex switching topology than I had hoped.

Here is the lstopo output for my 2 r9700s using 2 of the prom21 chips nvme slots. c5 and c9 are the r9700 cards.
Prom21 → nvme1/2 → occulink → minisforum dock → r9700 pro c5/c9

Tensor parallel performance of qwen 3.8 27B UD_Q8 using llama.cpp drops from 25tps decode using a dumb bifurcated 2x occulink card to 17tps decode using the prom21.