Hello!
I’m looking into buying a system for running inference with small to medium size LLM models. I wonder, is there any AM5 CPU + Chipset combination that supports 2x PCIe 16x with all lanes connected directly to the CPU? From what I’ve gathered my understanding is that there is no such configuration because the Ryzen 7000/9000 only have 24 PCIe lanes at best. This means I have to go for a Threadripper configuration, which is much more expensive. (The ROCm mGPU documentation states that all lanes shall be connected directly to the CPU.)
It’s possible that I can manage running two GPUs with 8x lanes, but it’s for sure not optimal…
But the thing is, it is quite hard for me to navigate the AMD website and the websites of various motherboard producers. I might very well be wrong.
So again: Is there any AM5 CPU + chipset combination that supports 2x PCIe 16x with all lanes connected directly to the CPU?
The AM5 chipset only supports up to 28.
That being said, performance loss depends on your inference engine. You could try and find a older threadripper to get proper 2x 16x, but you’d still be spending a pretty penny for PCIe Gen 4.
Unfortunately, whole gen 5 is twice the bandwidth as gen 4, 2x 8x PCIe 5 doesn’t become 2x 16x PCIe 4, though that would have been nice.
That’s what I thought. Thanks. The specification says that only 24 of the 28 lanes are available. Do you know why?
4 lanes are usually reserved for internal PCIe devices.
Is there any AM5 CPU + chipset combination that supports 2x PCIe 16x with all lanes connected directly to the CPU?
No, because the CPU doesn’t have that many PCIe lanes on it. There are only 24 on the CPU socket.
However… They are Gen5 lanes and potentially twice the speed of gen4. So, you can get X870 boards which have two x8 gen5 slots. Very few gpus are gen5 yet though.
