What every AI engineer needs to know about GPUs — Charles Frye, Modal
Jul 20, 2025 · 19:52
Charles Frye of Modal explains that AI engineers need to understand GPU hardware constraints to optimize inference, arguing GPUs embrace bandwidth over latency and that Tensor Cores for low-precision matrix-matrix multiplication are the key resource. He describes how GPUs achieve 16,000+ parallel threads per cycle on H100, and notes Patterson’s Law: bandwidth improves at the square of latency. The main insight: arithmetic intensity favors N² operations per N memory loads, so matrix-matrix operations are efficient while matrix-vector is wasteful. Frye demonstrates that running a small 8B model 1,000 times on the same prompt matches GPT-4 quality, and that multi-token prediction and multi-sample query become nearly free because Tensor Cores handle expanded batches as matrix-matrix multiplications. He recommends using smaller models that fit on a single GPU and scaling via multiple generations.
