The Synthesis Microbenchmark Investigation: A Systematic Codebase Reconnaissance in the SUPRASEAL_C2 Pipeline

Introduction

In the high-stakes world of Filecoin proof generation, where a single Groth16 proof for a 32 GiB sector consumes approximately 200 GiB of peak memory and involves a complex call chain from Go orchestration through Rust FFI into C++/CUDA GPU kernels, performance regressions are costly and difficult to diagnose. When a mysterious 5–6 second slowdown struck the SUPRASEAL_C2 pipeline during Phase 4 optimization work, the team needed a precise diagnostic instrument: a standalone microbenchmark that could measure only the CPU-bound circuit synthesis step, entirely decoupled from GPU computation, SRS parameter loading, daemon communication, and gRPC overhead.

This article synthesizes the work captured in messages 0 through 8 of a subagent session (session 392) within segment 13 of the broader SUPRASEAL_C2 investigation. The individual messages have been analyzed in depth across nine companion articles [1][2][3][4][5][6][7][8][9], each examining a specific message's role in the investigation. What unfolds across these nine messages is a masterclass in systematic codebase reconnaissance — a methodical tracing of dependency chains, feature gates, and public API surfaces across three Rust crates, culminating in a precise, actionable blueprint for the synth-only microbenchmark. The investigation demonstrates how disciplined information gathering, parallel exploration, and incremental knowledge accumulation can transform a complex architectural question into a clear engineering plan.

The Broader Context: A Regression Under the Microscope

The root session of this investigation had been conducting a deep-dive analysis of the SUPRASEAL_C2 Groth16 proof generation pipeline for Filecoin Proof-of-Replication (PoRep). Through Phases 0 through 3, the team had established a solid baseline of 88.9 seconds for a single 32 GiB PoRep proof. Then came Phase 4 Wave 1, a set of five optimizations applied simultaneously:

The Investigation: A Seven-Message Systematic Reconnaissance

What follows across messages 1 through 7 is a textbook demonstration of methodical codebase investigation. Each message builds on the previous one, filling specific knowledge gaps identified in the prior round.

Phase 1: Orientation (Message 1)

The assistant's opening move ([msg 1]) is deceptively simple: four parallel glob calls to confirm that all four target files exist at the expected paths. This orientation step is critical — jumping straight into reading files without first confirming their existence would risk wasted effort on error handling. The assistant's choice of glob over read is deliberate: a glob on a non-existent file gracefully returns zero results, while a read would produce an error. The parallel dispatch of all four globs in a single round minimizes latency, leveraging the opencode session model where tools within a round are dispatched simultaneously.

The glob results confirm that all four files exist at the expected paths under /home/theuser/curio/extern/:

Phase 2: Broad Reading (Message 2)

With file existence confirmed, the assistant proceeds to read all four files in parallel ([msg 2]). This is a deliberate strategy: there is no ordering dependency between the reads, so parallelizing them saves multiple round-trips. The assistant communicates the transition explicitly: "Good, all four files exist. Let me read them all in parallel."

The reads reveal the high-level structure:

Phase 3: Deepening (Messages 3–4)

After the broad read, the assistant identifies two critical gaps: the exact definition of the C1OutputWrapper struct (the JSON deserialization target for the C1 input) and the precise re-export path of synthesize_circuits_batch through bellperson's module hierarchy.

In message 3, the assistant greps for pub struct C1OutputWrapper and finds it at line 40 of cuzk-core/src/prover.rs. It also attempts to grep for the re-export path of synthesize_circuits_batch using the pattern pub (mod|use).*synthesize_circuits_batch, which returns no matches — a negative result that signals the re-export path is non-trivial. The assistant also reads cuzk-core/Cargo.toml to understand its dependency surface.

Message 4 drills deeper. The assistant reads prover.rs to see the C1OutputWrapper struct definition and its doc-comment, which reveals the JSON schema: SectorNum, Phase1Out (a base64-encoded JSON blob of SealCommitPhase1Output), and SectorSize. The assistant also greps for pub.*synthesize_circuits_batch (a broader pattern) and finds two matches at lines 144 and 164 of supraseal.rs — the standard batch synthesis function and its _with_hint variant.

Phase 4: Tracing the Dependency Chain (Messages 5–7)

With the function located, the assistant now needs to verify the full chain of accessibility from cuzk-bench to synthesize_circuits_batch. This requires checking three links:

Link 1: The re-export path in bellperson. Message 5 greps bellperson/src/groth16/mod.rs for synthesize_circuits_batch|prove_from_assignments and finds the function re-exported at line 34, confirming it is part of the public API as bellperson::groth16::synthesize_circuits_batch. The assistant also reads the workspace root Cargo.toml, confirming that cuzk-core is a workspace dependency and cuzk-bench is a workspace member — meaning adding cuzk-core as a dependency is a single-line change.

Link 2: The feature gate. Message 6 reads bellperson/src/groth16/mod.rs directly and confirms that the entire prover module — and thus synthesize_circuits_batch — is gated behind #[cfg(feature = "cuda-supraseal")]. This is a critical finding: any crate calling this function must enable the cuda-supraseal feature, which transitively pulls in CUDA headers and GPU library dependencies. The assistant also confirms that cuzk-core/src/lib.rs declares pub mod pipeline; unconditionally.

Link 3: Module visibility in cuzk-core. Message 7 reads cuzk-core/src/lib.rs to verify that the pipeline module is not feature-gated at the module level. The confirmation — a simple pub mod pipeline; with no #[cfg] attribute — means that cuzk-bench can depend on cuzk-core and access its pipeline functions without needing to enable any special feature flags at the cuzk-core level (though the underlying bellperson functions still require cuda-supraseal).

The Synthesis: Message 8's Comprehensive Analysis

With all seven investigative messages complete, the assistant produces the final analysis report in message 8. This message is a masterclass in architectural synthesis, answering the user's four questions with precision and providing a complete blueprint for the microbenchmark.

What the Pipeline Functions Do

The assistant identifies the two logical steps in synthesize_porep_c2_batch (pipeline.rs lines 633–763):

Step A — Circuit Construction (CPU, non-trivial): Deserializes the C1 JSON wrapper (C1OutputWrapper), base64-decodes the inner SealCommitPhase1Output, builds PoRep setup parameters and compound public parameters, then iterates over all 10 partitions calling StackedCompound::circuit() for each. These are Filecoin-specific Stacked DRG (Depth Robust Graph) circuits for 32 GiB sectors.

Step B — Constraint Synthesis (CPU, heavy): Calls bellperson::groth16::synthesize_circuits_batch(circuits), which performs the actual R1CS witness generation using rayon-based parallelization across circuits. This is the step the microbenchmark aims to isolate.

The Function Signatures

The assistant provides two levels of the function:

Bellperson level (raw, generic):

bellperson::groth16::synthesize_circuits_batch<Scalar, C>(circuits: Vec<C>)

cuzk-core level (Filecoin-specific):

cuzk_core::pipeline::synthesize_porep_c2_batch(
    vanilla_proof_json: &[u8], sector_number: u64, 
    miner_id: u64, job_id: &str
) -> Result<SynthesizedProof>

cuzk_core::pipeline::synthesize_porep_c2_partition(
    vanilla_proof_json: &[u8], sector_number: u64, 
    miner_id: u64, partition_index: usize, job_id: &str
) -> Result<SynthesizedProof>

Both are gated behind #[cfg(feature = &#34;cuda-supraseal&#34;)].

The Dependency Recommendation

The assistant presents two options and recommends Option A:

Option A — Depend on cuzk-core (recommended, ~5 lines in Cargo.toml): Add cuzk-core = { workspace = true } as a dependency, gated behind a synth-bench feature that enables cuzk-core/cuda-supraseal. This leverages existing abstractions and minimizes code duplication.

Option B — Duplicate the circuit construction (not recommended): Would require manually adding all transitive dependencies (filecoin-proofs, bellperson, blstrs, ff, rayon, etc.) — essentially replicating what cuzk-core already provides.

The Code Size Estimate

The assistant estimates approximately 60–80 lines of new Rust code plus 5–6 lines of Cargo.toml changes. The breakdown:

The Timing Strategy

The assistant identifies a subtle but important nuance: the SynthesizedProof result already contains a synthesis_duration: Duration field that covers only the bellperson synthesis call, not the deserialization and circuit construction. This means the microbenchmark can get both total wall time (via Instant::now()) and pure bellperson synthesis time (via the built-in field) from a single run.

The Broader Significance

This investigation is remarkable not just for its thoroughness but for what it represents in the context of the larger SUPRASEAL_C2 effort. The synth-only microbenchmark was the diagnostic tool that would eventually isolate the SmallVec optimization (A1) as the cause of the 5–6 second regression, enabling the team to revert it and recover the baseline performance.

But beyond the immediate regression-hunting goal, this session produced a reusable architectural analysis framework. The dependency map, the function signatures with feature gate annotations, the timing strategy, and the code size estimate are all valuable for anyone working on the cuzk proving pipeline. The investigation methodology — start broad, read in parallel, trace dependencies, check conditional compilation, verify workspace configuration, and only then synthesize — is transferable to any large codebase investigation.

The work also surfaced several architectural insights that would inform the broader optimization effort:

Conclusion

The nine messages of this subagent session represent a complete arc of systematic investigation: from the user's precise question, through methodical file discovery and reading, through targeted deep-dives into struct definitions and feature gates, to a comprehensive synthesis that answers every question with actionable precision. The assistant's methodology — parallelizing independent operations, verifying assumptions at the source, tracing every link in the dependency chain, and never accepting a negative result as conclusive without follow-up — is a model for codebase reconnaissance at scale.

In the end, this session produced not just an analysis but a blueprint. The synth-only microbenchmark that would emerge from this investigation would go on to identify the SmallVec regression, enabling the team to continue optimizing the SUPRASEAL_C2 pipeline toward its goal of efficient, memory-savvy proof generation for Filecoin's decentralized storage network. And the methodology itself — the systematic, evidence-based approach to understanding unfamiliar code — stands as a lasting contribution to the practice of performance engineering.## References

[1] "The Architecture of a Question: Deconstructing a Microbenchmark Specification" — Analysis of the user's opening message (msg 0), examining how the question itself encodes a theory of the problem and a precise specification for the diagnostic instrument needed.

[2] "The Opening Move: A Study in Systematic Investigation" — Analysis of message 1, examining the parallel glob operation that confirmed all four target files exist before reading began.

[3] "The Parallel Read: A Transitional Moment in a Deep-Dive Investigation" — Analysis of message 2, examining the decision to read all four files in parallel and how this bridges reconnaissance and analysis.

[4] "The Investigative Pivot: Tracing a Function's Export Path in the cuzk Proving Stack" — Analysis of message 3, examining the pivot from breadth-first exploration to depth-first resolution of the C1OutputWrapper struct and the synthesis function's re-export path.

[5] "The Art of the Targeted Grep: Uncovering Synthesis Bench Prerequisites in a Groth16 Proving Pipeline" — Analysis of message 4, examining the targeted reads that extracted the C1OutputWrapper struct definition and the exact function signatures.

[6] "The Connecting Thread: How Two File Reads Unlocked a Microbenchmark's Dependency Map" — Analysis of message 5, examining how the re-export path verification and workspace Cargo.toml read tied together the dependency map.

[7] "Tracing the Dependency Chain: Verifying Feature Gating for a Synthesis Microbenchmark" — Analysis of message 6, examining the critical verification that synthesize_circuits_batch is gated behind #[cfg(feature = &#34;cuda-supraseal&#34;)].

[8] "The Gate Check: Verifying Module Accessibility in a Rust Codebase Investigation" — Analysis of message 7, examining the verification that the pipeline module in cuzk-core is unconditionally compiled.

[9] "The Architecture of a Microbenchmark: Dissecting the PoRep C2 Synthesis Pipeline" — Analysis of message 8, examining the comprehensive synthesis report that answered all four user questions with actionable precision.