The Baseline Threshold: Validating Phase 3 Cross-Sector Batching Through Empirical Measurement

Message 709 marks a pivotal transition in the cuzk SNARK proving engine project — the moment when weeks of architecture, implementation, and code review give way to empirical validation. The message is deceptively brief, containing only a single bash command that launches a memory monitor alongside the cuzk daemon. But this simplicity belies the dense accumulation of engineering decisions, infrastructure setup, and measurement discipline that make this single line possible.

The Message

**Test 1: Baseline — single proof, batch_size=1 (Phase 2 compatibility)**

Start the daemon and memory monitor:
[bash] nohup /tmp/cuzk-memmon.sh /tmp/cuzk-mem-baseline.csv 1 > /tmp/cuzk-memmon-baseline.log 2>&1 &
echo "memmon PID: $!"
memmon PID: 2693813

Context and Motivation

To understand why this message was written, we must trace back through the preceding conversation. The cuzk project had just completed Phase 3 — cross-sector batching — a significant architectural enhancement to the pipelined SNARK proving engine. The core innovation was a BatchCollector ([msg 694]) that accumulates same-circuit-type proof requests (PoRep, SnapDeals) and flushes them when either max_batch_size is reached or max_batch_wait_ms expires. This allows multiple sectors' proof generation to share a single synthesis pass and GPU proving session, amortizing fixed costs and improving GPU streaming multiprocessor utilization.

The implementation had been committed in 1b3f1b39 on the feat/cuzk branch, with 6 files changed, 1134 lines added, and 170 lines removed ([msg 691]). All 25 unit tests passed with zero warnings. But passing unit tests is not the same as working on real hardware with real GPU proving. The user's instruction was unambiguous: "Proceed to test" ([msg 695]). And the user added a critical requirement: "for testing also record avg/peak ram memory use" ([msg 702]).

This message is the first concrete action in response to that directive. It represents the beginning of a carefully structured test protocol designed to answer three questions: Does Phase 3 batching work on real GPU hardware? What throughput improvement does it deliver? And what is the memory cost of that improvement?

The Baseline Strategy

A key design decision visible in this message is the choice to start with a baseline measurement using batch_size=1. This is not an arbitrary starting point — it serves dual purposes. First, it validates that the Phase 3 implementation is backward compatible with Phase 2 behavior. The entire batching architecture is designed so that max_batch_size=1 (the default) preserves the exact same single-sector pipeline behavior as before. Running this test first confirms that the refactored engine, with its new BatchCollector, synthesize_porep_c2_multi(), and split_batched_proofs() functions, does not regress when batching is disabled.

Second, the baseline provides the essential comparison point. Without knowing how long a single proof takes and how much memory it consumes, the throughput and memory overhead of batch_size=2 would be meaningless numbers. The assistant is establishing a controlled experiment: measure the independent variable (single proof performance) before introducing the experimental treatment (batching multiple proofs).

The Memory Monitor Infrastructure

The user's request to record memory usage prompted the assistant to write a dedicated monitoring script (/tmp/cuzk-memmon.sh) in [msg 706]. This script polls the daemon process's RSS from /proc at regular intervals and writes timestamped samples to a CSV file. The choice of RSS (Resident Set Size) as the metric is significant — it captures the actual physical memory consumed by the process, including the ~44 GiB of SRS (Structured Reference String) parameters that are pinned in GPU memory. This is the most relevant metric for understanding the real-world cost of running the proving engine on a machine with finite RAM.

The script is launched with nohup and backgrounded with &, ensuring it survives the shell session and continues recording independently of the test commands. The CSV file path (/tmp/cuzk-mem-baseline.csv) and log file (/tmp/cuzk-memmon-baseline.log) are parameterized, allowing multiple test runs to produce separate datasets without overwriting each other. The PID (2693813) is captured for later management — the assistant will need to kill this process after the test completes.

Assumptions Embedded in This Message

Several assumptions underpin this seemingly simple command. The assistant assumes that the memory monitor script was correctly written and is executable (it had just run chmod +x in [msg 707]). It assumes the baseline config file (/tmp/cuzk-baseline-test.toml) was correctly written in [msg 708] with max_batch_size=1. It assumes the CUDA-enabled release binary was successfully built in [msg 699]. It assumes the test data (/data/32gbench/c1.json) and SRS parameters (/data/zk/params) are present and valid, as verified in [msg 698].

Perhaps the most subtle assumption is that the memory monitor should be started before the daemon. This means the monitor will initially record zero RSS until the daemon process appears and begins allocating memory. This is actually a deliberate choice — it captures the full lifecycle including SRS loading, which takes approximately 15 seconds and consumes ~44 GiB of pinned memory. Starting the monitor first ensures no allocation phase is missed.

What This Message Does Not Show

The message ends with the memory monitor PID. The daemon itself has not been started yet — that happens in the very next message ([msg 710]), where cuzk-daemon --config /tmp/cuzk-baseline-test.toml is launched with nohup. This separation is important: the assistant is proceeding step by step, ensuring each component is properly initialized before the next begins. The memory monitor must be running before the daemon starts, or the initial SRS loading phase would be missed.

The actual proof submission — running cuzk-bench single -t porep --c1 /data/32gbench/c1.json — occurs in [msg 713], three messages later, after the daemon has finished loading the SRS and reported "cuzk engine started." This careful sequencing reflects an understanding that the proving engine requires significant initialization (SRS loading, GPU worker pool setup) before it can accept requests.

The Results This Baseline Enabled

The baseline test completed in 88.9 seconds total (synthesis 59.3s, GPU 28.8s) with approximately 5.5 GiB RSS memory ([chunk 11.1]). This established the reference point against which the batch_size=2 test would be compared. When the batched test later completed two proofs in 121.6 seconds total (60.8s per proof steady-state) with peak RSS of approximately 7.5 GiB, the improvement was clear: a 1.46x throughput increase with only ~2 GiB additional memory overhead. The memory efficiency was far better than the theoretical 2x because the SRS (47 GiB pinned) is shared across all proofs in the batch, and only the compressed auxiliary assignments grow linearly with batch size.

Engineering Philosophy

This message reveals a methodical engineering approach. The assistant does not jump directly to testing the new batching feature. Instead, it first establishes a baseline, validates backward compatibility, and instruments the measurement infrastructure. The memory monitor script, the separate config files for baseline and batch tests, the careful sequencing of process launches, and the logging of PIDs for cleanup — all reflect a disciplined testing methodology.

The message also demonstrates the importance of measurement in performance engineering. The cross-sector batching optimization was designed to improve throughput, but the magnitude of that improvement and its memory cost could only be determined through empirical measurement on real hardware. By instrumenting memory usage from the start, the assistant ensured that the optimization would be evaluated not just on speed but on its full resource profile — a critical consideration for a system designed to run on rented cloud GPUs where memory is a constrained and costly resource.

Conclusion

Message 709 is a threshold moment — the point where theory meets practice, where code meets hardware, where design meets measurement. A single bash command launching a memory monitor encapsulates hours of implementation work, careful architectural decisions, and a disciplined approach to empirical validation. The baseline it establishes will serve as the reference point for evaluating the entire Phase 3 batching optimization, providing the data needed to confirm that the 1.46x throughput improvement comes at an acceptable memory cost. In the broader arc of the cuzk project, this message represents the transition from builder to measurer, from architect to experimentalist — a shift that is essential for any serious performance engineering effort.