Chunk 13.0
The current chunk focuses on a critical performance regression encountered during Phase 4 of the cuzk project. While Phases 0 through 3 were successfully completed, establishing a strong baseline of 88.9 seconds for a single 32 GiB PoRep proof, the initial application of Phase 4 Wave 1 optimizations resulted in a significant slowdown to 106 seconds. The immediate task is to systematically diagnose this regression using detailed CUDA timing instrumentation (`CUZK_TIMING` printf's) that has been added to the GPU code to enable precise micro-benchmarking and A/B testing. Five optimizations were implemented (A1 SmallVec, A2 Pre-sizing, A4 Parallel B_G2, B1 cudaHostRegister, D4 Per-MSM window), but the regression analysis strongly implicates two primary suspects. B1's memory pinning is suspected of adding overhead by touching every page of ~120 GiB of host memory, while A2's upfront allocation of massive vectors appears to cause a page-fault storm. A2 has already been partially reverted in the multi-sector synthesis path, but one remaining call site in the pipeline still needs to be fully reverted. The other changes—A1, A4, and D4—are considered low-risk or neutral for the single-circuit test case. All Phase 4 changes remain uncommitted to git, pending the outcome of the diagnostic tests. The immediate plan is to finish reverting A2, rebuild with the instrumented CUDA code, and run a single-proof test to obtain a precise phase-level timing breakdown. This data will determine which optimizations are kept (likely A1, A4, D4) and which are reverted (likely B1). The overarching theme of this chunk is disciplined performance engineering: implementing a suite of changes, measuring the holistic impact, diagnosing regressions through detailed instrumentation, and having the rigor to revert harmful changes. The ultimate goal is to commit a clean, validated set of Phase 4 Wave 1 optimizations that strictly improve upon the established baseline.