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Building a personal, private AI computer on a budget

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Re: Building a personal, private AI computer on a budget

#71

Pay attention to IO bandwidth if you’re building a machine with multiple GPUs like this! In this setup the model is sharded between cards so data must be shuffled through a PCIe 3.0 x16 link which is limited to ~16 GB/s max. For reference that’s an order of magnitude lower than the ~350 GB/s memory bandwidth of the Tesla P40 cards being used. Author didn’t mention NVLink so I’m presuming it wasn’t used, but I believe…

I feel that you are mistaking the two bandwidth numbers

Re: Building a personal, private AI computer on a budget

#72

Pay attention to IO bandwidth if you’re building a machine with multiple GPUs like this! In this setup the model is sharded between cards so data must be shuffled through a PCIe 3.0 x16 link which is limited to ~16 GB/s max. For reference that’s an order of magnitude lower than the ~350 GB/s memory bandwidth of the Tesla P40 cards being used. Author didn’t mention NVLink so I’m presuming it wasn’t used, but I believe…

Unless you run the GPUs in parallel, which you have to go out of your way to do, the IO bandwidth doesn't matter. The cards hold separate layers of the model, they're not working together. They're only passing a few kilobytes per second between them.

Re: Building a personal, private AI computer on a budget

#73

Pay attention to IO bandwidth if you’re building a machine with multiple GPUs like this! In this setup the model is sharded between cards so data must be shuffled through a PCIe 3.0 x16 link which is limited to ~16 GB/s max. For reference that’s an order of magnitude lower than the ~350 GB/s memory bandwidth of the Tesla P40 cards being used. Author didn’t mention NVLink so I’m presuming it wasn’t used, but I believe…

Which models do you enjoy most on your 4090? and why vLLM instead of ollama?

Re: Building a personal, private AI computer on a budget

#75
post #20

Earlier quoted context omitted.

Runs is an overstatement though. With 4 tokens/second you can't use it on production.

Isn’t 4 tps good enough for local use by a single user, which is the point of a personal AI computer?

It is for me. I'm happy to switch over to another task (and maybe that task is refilling my coffee) and come back when the answer is fully formed.

Re: Building a personal, private AI computer on a budget

#77

I doubt it is that efficient. Even though it has 48GB of VRAM, it's more than twice slower than a single 3090 GPU. In my budget AI setup I use 7840 Ryzen based miniPC with USB4 port and connect 3090 to it via the eGPU adapter (ADT-link UT3G). It costed me about $1000 total and I can easily achieve 35 t/s with qwen2.5-coder-32b using ollama.

Wouldn't eGPU defeat the purpose of having fast memory bandwidth? Have you tried it with stable diffusion?

Re: Building a personal, private AI computer on a budget

#78

Earlier quoted context omitted.

I tried running the 8B model on my 8GB M2 Macbook Air through Ollama and it was awful. It took ages to do anything and the responses were bad at best.

Doesn't 8B need at least 16gb of ram? Otherwise, your swapping I would imagine...

Depends on quantization selected - see https://www.canirunthisllm.net/

Re: Building a personal, private AI computer on a budget

#79
post #56

Earlier quoted context omitted.

> expensive to run on an overbuilt machine There's a healthy secondary market for GPUs.

The price goes up dramatically once you go past 12GB though, that’s the problem.

Not on these server GPUs.

I'm seeing 24GB M40 cards for $200, 24GB K80 cards for $40 on eBay.

Re: Building a personal, private AI computer on a budget

#80
post #4

Great breakdown!. The "own your own AI" at home is a terrific hobby if you like to tinker, but you are going to spend a ton of time and money on hardware that will be underutilized most of the time. If you want to go nuts check out Mitko Vasilev's dream machine. It makes no sense if you don't have a very clear use case that only requires small models or really slow token generation speeds. If the goal however is not…

Terrific hobby? Sign me up!
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