Practical limit hit. Decoding so fast that tool calls (cpu) starting to become real limit not decode or prefill. Single RTX5090. Porting Kenshi to Godot project.

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Summary

A developer shares their experience discovering that when running 25 concurrent coding agents on an RTX 5090 GPU, the CPU (9800X3D) becomes the primary bottleneck for tool-call execution rather than GPU decode speed. They also share practical lessons on front-end tuning and agent slot management.

Hi folks, LIVE PROJECT PAGE TLDR: Moral of the story. You need better CPU to do actual agentic coding doing real work... I've been on a mission to make my RTX5090 go brrr for past 2 months so much so that i made my own engine for it which received "warm" welcome here (yeah, source is coming) After recent upgrades to how cache is stored and how i can reused some of prefills for other jobs that share initial same prefill i pretty much started to see degradation the more agents I started to add to project which started to use 12 slot server. Actual server started to be underutilized. Free context, free slots, gpu chilling at average of ~700t/s doing real work (no greedy code, but also thinking tool calls, etc.) and I couldn't figure out what was going on... I make it faster and faster, better handle jobs and it slows down... I've run 25 agents at the same (to properly fill the 12 slots) time and almost all of them soon started to set on `tool call` and my server started to barely work. I've finally checked task manager but not gpu or memory but cpu. And there it was. 100% every thread completely chocked. Lesson. If you want to do agentic coding with actual use of tools you need to make sure your CPU is up to task. My 9800X3D is just not enough to keep up with tool work for this project with heavy agents use despite engine being more than capable of going faster. edit: Some more lessons: - Tuning your front end makes ton of sense. Before I tuned it it was shoveling 20k prompts, after tuning barely 7k as new jobs and better more compact tasks. Wall time went from 43minutes to 18 minutes before/after rework of front end. - Always keep more agents than server has slots for inevitable pauses due to tool use/tests etc. - Shared context is superior choice to fixed context every time i tried it over course of the project.
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