The Final Cut: Replacing get_pce() in the cuzk Benchmark Suite

In the sprawling refactoring of the cuzk GPU proving engine's memory management, most of the dramatic changes happened in the core engine — rewriting the start() method, wiring evictor callbacks, implementing two-phase GPU memory release, and replacing static concurrency limits with budget-based admission control. But every architectural overhaul leaves a trail of smaller, less glamorous fixes in its wake: updating configuration files, adjusting function signatures, and — as seen in this message — replacing a single removed function call in a benchmarking utility.

The subject message is deceptively brief:

[assistant] Now update the get_pce call at line 1248: [edit] /tmp/czk/extern/cuzk/cuzk-bench/src/main.rs Edit applied successfully.

Fourteen words of narration, one edit command, and a confirmation. Yet this message represents the culmination of a long chain of reasoning about dependency management, API boundaries, and the relationship between a library and its downstream consumers. To understand why this edit exists at all, one must trace the entire arc of the memory manager integration.

The Architecture That Was

Before the memory manager refactoring, the cuzk proving engine used a set of static OnceLock-based caches for Pre-Compiled Constraint Evaluators (PCEs). These were global singletons, accessible from anywhere in the codebase via pipeline::get_pce(). The function was simple: it looked up a CircuitId in a static HashMap and returned a reference to the cached PCE data. This design had the virtue of simplicity — any module that needed a PCE could just call get_pce() without worrying about ownership, lifetimes, or initialization order.

But it had a critical flaw: it was invisible to the memory manager. The global caches held GPU memory that could not be accounted for, budgeted, or evicted. As the proving engine scaled to handle larger proofs and more concurrent workloads, this became untenable. The solution was a PceCache struct — a budget-aware, evictable cache that could be passed explicitly through the pipeline, allowing the memory manager to track and control GPU memory consumption.

The Ripple Effect of API Changes

When pipeline::get_pce() was removed and replaced with PceCache, every call site needed updating. The assistant had already converted all five dispatch_batch call sites in engine.rs, updated the SynthesizedJob construction paths, and rewritten the GPU worker loop. But the changes did not stop at the library boundary.

The cuzk-bench binary is a standalone testing and benchmarking utility that exercises the proving pipeline directly, without going through the Engine abstraction. It calls cuzk_core::pipeline::extract_and_cache_pce_from_c1() to extract PCE data from a C1 proof output, and then — if the --save-pce flag is provided — retrieves the cached PCE via get_pce() to write it to disk. Both of these calls were broken by the refactoring.

The assistant discovered this in message 2226, when a grep for get_pce revealed the lingering reference in the bench code. The grep output showed:

Line 1248:         let pce_ref = cuzk_core::pipeline::get_pce(&cuzk_core::srs_manager::CircuitId::Porep32G)

This line would fail to compile after the refactoring. The function no longer existed.

The Reasoning Chain

The assistant's thinking process reveals a careful consideration of the bench's architectural position. Unlike the engine, which owns an SrsManager and a MemoryBudget, the bench is a thin command-line wrapper. It does not create an Engine — it calls pipeline functions directly. This means it cannot rely on the engine's PceCache instance; it must create its own.

In message 2233, the assistant addressed the extract_and_cache_pce_from_c1 call site, which now requires a &PceCache parameter. The reasoning was explicit: "The bench function needs a PceCache. I'll create one at the start of each bench function. Since the bench doesn't have a runtime budget, I'll create a PceCache with a large budget." This decision reflects a pragmatic trade-off: the bench does not need fine-grained memory accounting, so a generously-sized cache suffices.

The subject message (2234) handles the second broken call site — the get_pce() retrieval for saving PCE data to disk. With the PceCache now available as a local variable in the bench function, the fix is straightforward: replace the static function call with a method call on the cache instance. Instead of pipeline::get_pce(&circuit_id), the code now uses pce_cache.get(&circuit_id).

Assumptions Embedded in the Fix

This edit rests on several assumptions, each worth examining. First, the assistant assumes that the PceCache created in the bench will contain the PCE data by the time the save-to-disk code runs. This is a reasonable assumption because extract_and_cache_pce_from_c1 is called earlier in the same function, which populates the cache. The ordering is deterministic — extraction happens first, then the optional save.

Second, the assistant assumes that PceCache::get returns a type compatible with the subsequent serialization code. The old get_pce() returned a &PreCompiledCircuit (or similar), and the new cache's get() method presumably returns the same type. If the cache stored wrapped or boxed variants, the downstream code would need adjustment. The edit succeeded without errors, validating this assumption.

Third, the assistant assumes that a single PceCache instance, shared across the entire bench function, is sufficient. This is correct because the bench processes one proof at a time — there is no concurrent access that would require separate caches or thread-local storage.

What This Message Represents

On its surface, this message is trivial: one function call replaced by another. But it represents something larger — the completion of a clean API migration. Every removed function must have all its call sites updated before the codebase compiles again. The assistant had already updated the core engine, the configuration file, and the SRS manager. The bench was the last consumer of the old API.

The message also illustrates a pattern common in large refactorings: the "long tail" of changes that follow a core architectural shift. The dramatic changes happen first — rewriting the engine, introducing new types, removing old abstractions. But the work is not done until every downstream consumer, every test utility, and every configuration file has been updated to match. This edit is the tail end of that process.

The Broader Significance

This edit completed the migration of the cuzk codebase from static, unaccounted PCE caches to explicit, budget-aware cache management. After this change, there were no remaining references to pipeline::get_pce(), preload_pce_from_disk(), or the old partition_workers configuration fields anywhere in the codebase. The todo list, updated in message 2221, marked the engine changes, config updates, and bench updates as complete.

The unified memory manager — with its MemoryBudget, MemoryReservation, two-phase release, and eviction support — was now fully integrated. The bench, though a minor utility, was an important validation target: if the bench compiled and ran correctly with the new APIs, it demonstrated that the library's public interface was coherent and usable without the engine's runtime infrastructure.

Conclusion

Message 2234 is a single edit, fourteen words of narration, and a confirmation of success. But it is also the final stitch in a large architectural seam. The removal of get_pce() and its replacement with PceCache::get() represents the shift from global, invisible state to explicit, budget-managed resources — a transition that touches every layer of the system, from the engine's admission control to the benchmark's disk-save routine. In the end, even the smallest edits tell the story of the largest changes.