Segment 21
This sub-session focused on diagnosing and addressing the GPU idle gap identified in previous benchmarks. The user implemented detailed waterfall timeline instrumentation, confirming a ~12s structural GPU idle gap per proof cycle caused by strictly sequential synthesis (38s) exceeding GPU time (27s). To close this gap, parallel synthesis was implemented by refactoring the engine's synthesis task loop to use a tokio::sync::Semaphore, allowing multiple proofs to be synthesized concurrently under a new synthesis_concurrency config parameter. Benchmarking showed that with synthesis_concurrency=2 and client concurrency -j 3, GPU utilization reached 99.3%, eliminating the idle gap, but overall throughput improved only modestly (~5-7%, from ~45.3s to ~42.2s per proof) due to CPU resource contention between parallel syntheses and the GPU prover's CPU-intensive b_g2_msm step. Over-aggressive concurrency (-j 4) caused catastrophic contention (60.2s/proof), while insufficient depth (-j 2) starved the pipeline. The analysis concluded that further throughput gains require reducing absolute CPU time of synthesis via Phase 5 Wave 2/3 optimizations or decoupling CPU workloads, rather than adding more parallelism to the existing architecture.