The AMD Radeon Instinct MI300A's Giant Memory Subsystem

Re:The AMD Radeon Instinct MI300A's Giant Memory Subsystem by lhl on Saturday January 18, 2025 @12:35PM (#42749897)

Getting to 50 tok/s for a big model requires not just memory, but also memory bandwidth. Currently, 1TB/s of MBW will get a 70B Q4 (~40GB) model to about 20-25 tok/s. The good thing is models continue to get smarter - today's 20-30B models beat out last years 70B models on most tasks and the biggest open models like DeepSeek-v3 might have lots of weights, but actually a relatively reasonable # of activations/pass.

You can test out your half the speed but w/ 64GB or more of memory w/ the latest Macs, AMD Strix Halo, or the upcoming Nvidia Digits, though. I suspect by the middle of the year there will be a bunch of options in the ~$3K range. Personally, I think I'd rather go for 2 x 5090s for 64GB of memory at 1.7TB/s than 96 or 128GB w/ only 250GB/s of MBW.

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Re:The AMD Radeon Instinct MI300A's Giant Memory Subsystem by sroussey on Saturday January 18, 2025 @12:48PM (#42749979)

A Mac with that memory will have closer to 500GB/s but your point still stands.

That said, if you just want to play around, having more memory will let you do more interesting things. I’d rather have that option over speed since I won’t be doing production inference serving on my laptop.

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Re:The AMD Radeon Instinct MI300A's Giant Memory Subsystem by lhl on Saturday January 18, 2025 @12:54PM (#42750021)

Yeah, the M4 Max actually has pretty decent MBW - 546 GB/s (cheapest config is $4.7K on a 14" MBP atm, but maybe there will be a Mac Studio at some point). The big weakness for the Mac is actually the lack of TFLOPS on the GPU - the beefiest maxes out at ~34 FP16 TFLOPS. It makes a lot of use cases super painful, since prefill/prompt processing can take minutes before token generation starts.

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