LLM Inference Is a Memory Problem, Not a Compute One

A model that fits on your GPU isn't necessarily a model you can serve to real users — and this video explains exactly why. Starting with a deceptively simple deployment that works perfectly for one person but grinds to a halt for three, the video walks through the real arithmetic of GPU inference: why weights are only half the story, what the KV cache actually is, and how it quietly becomes the constraint that limits every concurrent user on your hardware. Using a live deployment on a single NVIDIA L4 with a real load test, you can watch the failure happen in real time — and then watch it get fixed. The fix turns out to be four lines of configuration. Through weight quantization and KV cache quantization, the same card goes from supporting under three simultaneous conversations to over sixteen, with throughput roughly quadrupling across the full benchmark — no new hardware, no model swap, no purchase order. The video is honest about what that costs in quality, where the tradeoffs actually bite (multi-step reasoning and code generation), and why the throughput gains don't perfectly match what the engine's startup logs predict. By the end, you'll know how to read those logs before a single request arrives, why "does it fit" is the wrong question to ask about a GPU, and exactly which numbers to watch when you're deciding how many users your inference setup can actually serve. #GPUInference #KVCache #ModelQuantization Consider joining the channel: https://www.youtube.com/c/devopstoolkit/join ▬▬▬▬▬▬ 🔗 Additional Info 🔗 ▬▬▬▬▬▬ ➡ Transcript and commands: https://devopstoolkit.live/ai/why-your-gpu-fails-at-3-users-llm-inference-isnt-a-compute-problem ▬▬▬▬▬▬ 💰 Sponsorships 💰 ▬▬▬▬▬▬ If you are interested in sponsoring this channel, please visit https://devopstoolkit.live/sponsor for more information. Alternatively, feel free to contact me over Twitter or LinkedIn (see below). ▬▬▬▬▬▬ 👋 Contact me 👋 ▬▬▬▬▬▬ ➡ BlueSky: https://vfarcic.bsky.social ➡ LinkedIn: https://www.linkedin.com/in/viktorfarcic/ ▬▬▬▬▬▬ 🚀 Other Channels 🚀 ▬▬▬▬▬▬ 🎤 Podcast: https://www.devopsparadox.com/ 💬 Live streams: https://www.youtube.com/c/DevOpsParadox ▬▬▬▬▬▬ ⏱ Timecodes ⏱ ▬▬▬▬▬▬ 00:00 LLM Inference Memory 03:01 Model Weights VRAM Math 04:35 What Is A KV Cache 07:32 Watching vLLM Break Under Load 11:53 How Quantization Frees VRAM 16:01 What Quantization Costs You 19:42 Quantizing The KV Cache Inference Is A Memory Problem