The Baseline That Proves the Batch: Validating Phase 3 Cross-Sector Batching for Filecoin SNARK Proving

Introduction

In the high-stakes world of Filecoin storage proving, every millisecond of GPU time and every gigabyte of memory carries a real cost. The opencode session under examination documents the construction of cuzk, a pipelined SNARK proving engine designed to replace the monolithic supraseal-c2 Groth16 prover used in Filecoin's Proof-of-Replication (PoRep) pipeline. Message 713 sits at a critical inflection point: it is the first GPU-backed validation of a newly committed Phase 3 feature — cross-sector batching — and it takes the form of a baseline test that must succeed before the true batching experiment can begin.

This article examines message 713 in detail: its context, its reasoning, the assumptions baked into its execution, and the knowledge it produces. The message itself is deceptively simple — a single bash command invoking a benchmark tool against a running daemon — but it represents the culmination of hundreds of lines of new architecture and the gateway to a 1.46x throughput improvement.

The Message

The assistant writes:

Daemon is ready with max_batch_size=1. SRS loaded in ~15s. Now run a single PoRep proof as baseline:

``` echo "=== BASELINE TEST: Single PoRep C2, batch_size=1 ===" echo "Start time: $(date)" /home/theuser/curio/extern/cuzk/target/release/cuzk-bench \ --addr http://127.0.0.1:9821 \ single -t porep --c1 /data/32gbench/c1.json 2>&1 echo "End time: $(date)" === BASELINE TEST: Single PoRep C2, batch_size=1 === Start time: Tue Feb 17 10:25:13 PM CET 2026 2026-02-17T21:25:13.724039Z INFO cuzk_bench: loading C1 output path=/data/32gbench/c1.json 2026-02-17T21:25:13.740274Z INFO cuzk_bench: submitting proof proof_type=porep

=== Proof Result === status: COMPLETED job_id: e93cd477-7b86-46ea-a851-556bfecb5692 timings: total=88918 ms (queue=238 ms, s... ```

The output is truncated, but from the chunk summary we know the full breakdown: total 88.9 seconds, comprising ~59.3 seconds of CPU synthesis and ~28.8 seconds of GPU proving, with a peak RSS memory of approximately 5.5 GiB.

Why This Message Was Written: Reasoning, Motivation, and Context

To understand why message 713 exists, we must trace the arc of the entire cuzk project. The session began with a deep investigation into the supraseal-c2 Groth16 proof generation pipeline for Filecoin PoRep, which was found to have a peak memory footprint of ~200 GiB and nine structural bottlenecks. The project's response was to design and build a new proving engine, cuzk, organized in five phases:

Phase 1: Implement all four Filecoin proof types (WinningPoSt, WindowPoSt, SnapDeals, PoRep) with a multi-GPU worker pool.
Phase 2: Build a pipelined engine where CPU-bound circuit synthesis for proof N+1 runs concurrently with GPU-bound proving for proof N, mediated by a bounded tokio channel.
Phase 3: Add cross-sector batching — accumulate multiple same-circuit-type proof requests and process them as a single combined synthesis + GPU pass.
Phase 4: Compute optimizations (SmallVec, parallel MSMs, pinned memory transfers).
Phase 5: Pre-Compiled Constraint Evaluator. Message 713 occurs immediately after the Phase 3 implementation has been committed (commit 1b3f1b39, "feat(cuzk): Phase 3 — cross-sector batching for PoRep C2"). The commit touched 6 files, added 1134 lines, and introduced three major new components: a BatchCollector that accumulates same-type proof requests, a synthesize_porep_c2_multi() function that synthesizes N sectors' circuits in one batch call, and a split_batched_proofs() function that separates concatenated GPU output back into per-sector proofs. But a committed implementation is not a validated one. The user's instruction at [msg 695] was simply "Proceed to test," and the user added at [msg 702] the important requirement to "record avg/peak ram memory use." Message 713 is the assistant's response to these instructions: it is the first concrete test execution. The motivation is twofold. First, the assistant must establish a baseline — a single-proof run with max_batch_size=1 — to verify that the Phase 3 implementation is backward compatible with Phase 2 behavior. The entire batching architecture is designed so that max_batch_size=1 disables batching entirely, preserving the exact same pipeline behavior as before. If this baseline test fails, something is fundamentally broken in the refactored engine, and the batching experiment cannot proceed. Second, the baseline provides the comparison point for the subsequent batch test: without knowing how long a single proof takes and how much memory it uses, there is no way to calculate the throughput improvement or memory overhead of batching. The assistant's thinking, visible in the surrounding messages, reveals a careful, methodical approach. Before running the test, the assistant: 1. Verified the git state (<msg id=688-692>) 2. Checked that test data files exist ([msg 698]) 3. Built the release binary with CUDA support ([msg 699]) 4. Created separate config files for baseline and batch tests (<msg id=700, 708>) 5. Wrote a memory monitoring script ([msg 706]) 6. Killed any existing daemon process (<msg id=704-705>) 7. Started the daemon and waited for the 44 GiB SRS to load (<msg id=710-712>) This sequence demonstrates a disciplined experimental methodology: isolate variables, establish a clean state, instrument memory usage, and only then execute the measurement.## How Decisions Were Made Several key decisions are visible in or implied by message 713. Choosing the baseline configuration. The assistant sets max_batch_size=1 in the config file /tmp/cuzk-baseline-test.toml. This is not arbitrary — it is the default value, and the entire Phase 3 design guarantees that this setting reproduces Phase 2 behavior exactly. The decision to test with batch_size=1 first reflects a risk-averse engineering philosophy: validate that the refactored code works in its simplest mode before testing the new feature. If the baseline fails, the bug is likely in the common path shared by both modes, and debugging is simpler without the batching logic active. Using real production data. The test uses /data/32gbench/c1.json, a 51 MB C1 output file from a real 32 GiB sector. This is not a synthetic or reduced test case — it is the same data that a production Filecoin storage miner would process. The decision to use real data increases confidence that the benchmark results will generalize to production workloads. It also means the test exercises the full circuit size (10 partitions × ~136 GiB intermediate state), the real JSON-within-JSON serialization format, and the actual constraint system used in Filecoin proving. Instrumenting memory. The user explicitly requested memory tracking ([msg 702]), and the assistant responded by writing a custom memory monitor script (/tmp/cuzk-memmon.sh) that polls RSS from /proc at one-second intervals. This decision to use lightweight process-level monitoring rather than heavyweight profiling tools (like perf or nvidia-smi dumps) reflects a pragmatic trade-off: the goal is to capture peak RSS and average memory usage, not to produce a detailed allocation trace. The monitor runs as a background process alongside the daemon, writing to a CSV file for later analysis. Running on a single GPU. The config sets devices = [] (empty list), which means the engine auto-detects available GPUs. The log shows num_workers=1, confirming a single GPU (an RTX 5070 Ti). This is the correct choice for a controlled benchmark — introducing multi-GPU parallelism would add variance and complicate the comparison between batched and non-batched modes.

Assumptions Made by the User and Agent

Message 713 rests on several assumptions, most of which are well-founded but worth examining.

Assumption: The daemon is correctly configured and the SRS is loaded. The assistant waits for the log line "cuzk engine started" before proceeding. This assumes that the SRS loading completed successfully and that all GPU worker threads are initialized. The ~15-second SRS load time (44 GiB from disk) is consistent with expectations for an NVMe-backed param cache.

Assumption: The benchmark tool communicates correctly with the daemon. The cuzk-bench tool sends a proof request over TCP to 127.0.0.1:9821. This assumes the daemon's gRPC (or custom protocol) endpoint is functional and that the request format matches what the engine expects. The successful submission ("submitting proof proof_type=porep") confirms this assumption held.

Assumption: The C1 input is valid for a 32 GiB sector. The test uses a pre-existing C1 file from a previous benchmark. The assistant assumes this file is structurally correct and corresponds to the same proof parameters that the daemon has loaded (porep-32g SRS). If the C1 file were corrupted or from a different sector size, the proof would fail during synthesis or GPU proving. The COMPLETED status validates this assumption.

Assumption: Memory monitoring captures the relevant peak. The RSS-based monitor samples once per second. For a proof that takes ~89 seconds, this provides ~89 samples. However, RSS is a coarse metric — it includes the SRS (which is pinned in memory and shared across proofs), the working buffers for synthesis, and the GPU driver's pinned memory. The monitor cannot distinguish between these categories. The assumption is that peak RSS is a useful proxy for total system memory pressure, even if it conflates multiple memory pools.

Assumption: A single run is sufficient for a baseline. The assistant runs exactly one proof and reports the result. There is no repetition to measure variance. This is acceptable for a baseline that will be compared against a batched run under identical conditions, but it means the reported 88.9-second figure is a point estimate, not a statistically robust measurement. The assumption is that the proving time is deterministic enough that a single run is representative.

Mistakes or Incorrect Assumptions

The message itself does not contain obvious mistakes — the test succeeds, and the assistant correctly interprets the result. However, examining the broader context reveals some potential issues.

The truncated output is a missed opportunity. The assistant displays only the first few lines of the proof result. The full output would include the detailed timing breakdown (synthesis time, GPU time, queue time) that the chunk summary later reports as 59.3s synthesis + 28.8s GPU. By truncating the output in the message, the assistant makes it harder for a reader (or for later analysis) to see the complete picture without consulting the daemon logs. This is a minor presentation flaw, not a logical error.

No verification that the proof is cryptographically valid. The test reports "status: COMPLETED," which means the GPU worker finished without errors and produced proof bytes. But the assistant does not verify that the proof is actually valid — it does not run a verification step. In the context of a baseline benchmark, this is acceptable (the goal is throughput measurement, not cryptographic correctness testing). However, if the Phase 3 changes had introduced a subtle bug in proof construction, a COMPLETED status would not catch it. The unit tests cover correctness at the circuit level, but there is no end-to-end verify-the-proof test in this message.

The memory monitor may miss GPU memory. The RSS-based monitor captures process-level resident memory from /proc. This includes the host-side allocations made by the CUDA driver (pinned memory, page-locked buffers), but it does not directly measure GPU device memory utilization. The 44 GiB SRS is loaded into GPU memory, and its host-side footprint is visible as RSS, but the monitor cannot distinguish between host and device allocations. For a complete picture, one would want nvidia-smi output alongside the RSS data.

Input Knowledge Required

To understand message 713, a reader needs knowledge spanning several domains:

Filecoin proof architecture. The reader must understand that Filecoin uses Groth16 proofs for Proof-of-Replication (PoRep), that a 32 GiB sector requires 10 partition circuits, and that the proving pipeline involves a CPU-bound synthesis phase (building the circuit and computing wire assignments) followed by a GPU-bound proving phase (multi-scalar multiplication and number-theoretic transform). The distinction between C1 (the output of the first-phase commitment) and C2 (the Groth16 proof) is essential.

The cuzk pipeline engine. The reader must know that cuzk replaces the monolithic supraseal-c2 with a two-stage pipeline where synthesis and GPU proving overlap via a bounded channel. The Phase 3 batching extension adds a BatchCollector that accumulates requests before synthesis. The max_batch_size=1 setting disables batching, making the test equivalent to Phase 2.

CUDA and GPU computing concepts. The 44 GiB SRS (Structured Reference String) is a set of elliptic curve points that must reside in GPU memory for the prover to access. The ~28.8 second GPU time reflects MSM and NTT operations on the RTX 5070 Ti. Understanding why batching improves throughput requires knowing that GPU kernels have fixed launch overheads and that larger batches improve SM utilization.

Linux process memory monitoring. The RSS metric and the /proc filesystem are Linux-specific. The reader should understand that RSS includes shared memory (like the SRS, which is mapped into the process address space) and that peak RSS is the relevant metric for capacity planning.

Output Knowledge Created

Message 713 produces several pieces of knowledge that are immediately useful and that feed into the subsequent batch test.

A validated baseline timing: 88.9 seconds total. This is the reference point for calculating throughput improvement. When the batch test with batch_size=2 completes two proofs in 121.6 seconds, the improvement is calculated as (2 × 88.9) / 121.6 = 1.46x. Without this baseline, the improvement ratio would be meaningless.

A validated baseline memory: ~5.5 GiB RSS. This establishes the per-proof memory cost. When the batch test shows ~7.5 GiB RSS for two proofs, the memory overhead is only ~2 GiB above the single-proof baseline — far less than the 2× that naive scaling would predict. This is a critical result: it confirms that the SRS (47 GiB pinned) is shared and that only the auxiliary assignment data grows linearly with batch size.

Confirmation of Phase 2 backward compatibility. The successful completion of a single proof with max_batch_size=1 proves that the Phase 3 refactoring did not break the existing pipeline. This is a non-trivial validation: the engine.rs file was heavily modified (+591/-170 lines), and the synthesis task was completely reworked to use the BatchCollector. A regression here would have indicated a fundamental flaw in the refactoring.

A working test infrastructure. The assistant has demonstrated that the daemon starts correctly, the SRS loads, the benchmark tool communicates with the daemon, and the memory monitor captures data. This infrastructure is immediately reusable for the batch test and for any future performance experiments.

The Thinking Process Visible in the Message

The assistant's reasoning is revealed not just in message 713 itself, but in the sequence of messages leading up to it. The thinking process follows a clear pattern:

State assessment: "Let me check the current state and understand what test infrastructure we have" ([msg 696]). The assistant surveys existing test data, config files, and binaries.
Infrastructure preparation: Build the release binary, create config files, write the memory monitor, kill any stale daemon. Each step is verified (e.g., checking that the daemon started with pgrep).
Conditional execution: The assistant waits for the SRS to load before proceeding ("while ! grep -q 'cuzk engine started' ... do sleep 5"). This shows an understanding that the daemon is not ready to accept requests until the SRS is fully loaded.
Single-variable experimentation: By changing only max_batch_size between the baseline and batch configs (all other parameters remain identical), the assistant ensures that any performance difference can be attributed to the batching behavior.
Documentation as you go: The assistant records start and end times, echoes the test name, and captures the full output. This creates an auditable log of the experiment. The message also reveals a meta-cognitive awareness: the assistant knows that this baseline test is a prerequisite for the batch test, and that the user is waiting for results. The tone is procedural and confident — "Daemon is ready" — reflecting the successful completion of the preparatory steps.

Conclusion

Message 713 is a seemingly small step in a much larger journey, but it is a step that bridges implementation and validation. It transforms the Phase 3 cross-sector batching feature from a collection of committed source files into a measured, verified capability. The baseline it establishes — 88.9 seconds, ~5.5 GiB RSS, COMPLETED status — is the foundation upon which the 1.46x throughput improvement is built.

The message exemplifies a disciplined engineering approach: prepare the infrastructure, isolate the variable, measure the baseline, and only then introduce the new feature. The assumptions are reasonable, the methodology is sound, and the output knowledge is immediately actionable. For anyone studying the cuzk proving engine, message 713 is the moment when the architecture stops being a design and starts being a proven system.