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Advanced Micro Devices, Inc. (AMD) is an American multinational corporation and fabless semiconductor company that designs, develops and sells computer processors and related technologies for business and consumer markets.

AMD's main products include microprocessors, motherboard chipsets, embedded processors, and graphics processors for servers, workstations, personal computers, and embedded system applications. The company has also expanded into new markets, such as the data center, gaming, and high-performance computing markets. AMD's processors are used in a wide range of computing devices, including personal computers, servers, laptops, and gaming consoles.

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AM5 CPU + Chipset for 2+ GPUs? (self.amd)

submitted 1 week ago* (last edited 1 week ago) by sith to c/amd

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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?

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[–] [email protected] 4 points 1 week ago (1 children)

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.

[–] sith 1 points 1 week ago (1 children)

That's what I thought. Thanks. The specification says that only 24 of the 28 lanes are available. Do you know why?

[–] BrikoX 2 points 1 week ago

4 lanes are usually reserved for internal PCIe devices.