Chunk 25.0

The session began by consolidating the extensive uncommitted diff from the pinned memory pool work into two clean commits: one for the bellperson pinned backing and one for the cuzk pinned pool and reactive dispatch throttle. The user then critiqued the existing semaphore-based dispatch model, arguing it failed to maintain a stable pipeline because it limited total in-flight partitions rather than targeting a specific queue depth of synthesized partitions *waiting* for the GPU. The assistant implemented a P-controller by replacing the semaphore with a `Notify`-based two-phase loop: wait for a GPU completion event, then dispatch the full deficit in a burst to intentionally overshoot and converge on a steady state. The first deployment of this P-controller (`cuzk-pctrl1`) proved too aggressive, instantly filling all allocation slots. The user requested a dampening factor, capping the burst size at `max(1, min(3, deficit * 0.75))` to limit the expansion rate per GPU event. The assistant implemented this and deployed `cuzk-pctrl2`. However, the system remained unstable due to the deep synthesis pipeline, which made the raw waiting count a noisy and delayed feedback signal. The overarching theme of this chunk is the iterative refinement of a complex control system for GPU pipeline scheduling. The team moved from a simple reactive semaphore to a proportional controller, then to a dampened proportional controller. The user concluded the session by proposing a more sophisticated PI controller operating on a smoothed signal like an Exponential Moving Average (EMA) of the waiting count or GPU consumption rate to achieve stable, high-utilization scheduling with minimal memory pressure. The core pinned memory pool fix remains deployed and effective, but the dispatch scheduling logic is still under active development.

The Control System Odyssey: From Semaphore to PI Pacer in GPU Pipeline Dispatch 3165 words

Message Articles

Subagent Sessions