Problem

Main sumcheck was proved and verified per chip, which duplicated transcript work, selector/claim handling, and PCS opening plumbing across chips.

Design Rationale

Use one global batched main sumcheck proof while keeping PCS openings in the existing suffix path. The verifier mirrors the prover transcript order, including ECC bridge sampling before the global combine subset evals challenge, and evaluates frontloaded expressions in the verifier.

Change Highlights

• ceno_zkvm: batches main constraints into a single global proof path across chip proofs.
• ceno_zkvm: keeps witness/fixed PCS openings per chip after global main verification.
• ceno_recursion: mirrors native verifier changes for the batched main proof.
• ceno-gpu: supports the batched main proving flow.

Benchmark / Performance Impact

Benchmark session compares the frontload baseline against successive feat/batch_main_sumcheck optimization runs on block 23817600, GPU proving, CENO_GPU_ENABLE_WITGEN=0.

Comparison convention: lower time is better. Signed x values use -Nx for slower-than-baseline wall time and +Nx for faster/lower-time metrics; for example, taking twice as long is -2.00x.

Timeline / Optimization Progress

E2E / Layer

App Prove Breakdown

Profiler module totals can overlap because chip proving is concurrent; use app_prove wall time above for critical-path impact. The latest run materially reduces the new batched-main cost, but total wall time is still slower than the frontload baseline.

Latest Improvement Against Previous Batched Run

Benchmark command:

CENO_GPU_ENABLE_WITGEN=0 CENO_CONCURRENT_CHIP_PROVING=1 CENO_GPU_CACHE_LEVEL=0 \
RUSTFLAGS="-C target-feature=+avx2" \
cargo run --features "jemalloc,gpu" --release --bin ceno-reth-benchmark-bin -- \
  --mode prove-app --block-number 23817600 --rpc-url <redacted> \
  --output-dir output --cache-dir rpc-cache

Environment:

• GitHub self-hosted GPU runner, CUDA device cc=8.9, 24GB GPU memory.
• Rust nightly-2025-11-20, cargo 1.93.0-nightly.
• Baseline: run 25419833788 / job 74559223217, Ceno 7a07649b, GPU 1118dca8, summary.
• 2026-05-09 early batched branch: run 25594090744 / job 75136918384, Ceno dd229c00, GPU 340651b4, summary.
• 2026-05-09 batched-main critical path: run 25603601935 / job 75161599043, Ceno d5ae1b3a, GPU fbef26f3, summary.
• Latest optimization: run 25655529702 / job 75302942526, Ceno c2c45cc9, GPU 3dedbc78, summary.

Summary: latest optimization improves prove_batched_main_constraints by +1.74x against the previous batched-main run (26.925s -> 15.457s) and improves E2E by +1.13x (104.000s -> 91.800s). It remains slower than the frontload baseline (75.600s -> 91.800s, -1.21x), with the remaining gap concentrated in the new batched-main critical path.

Testing

RUST_MIN_STACK=33554432 cargo check --package ceno_recursion --bin e2e_aggregate
RUST_MIN_STACK=33554432 cargo run --release --package ceno_recursion --bin e2e_aggregate -- --platform=ceno --max-cycle-per-shard=1600 examples/target/riscv32im-ceno-zkvm-elf/release/examples/keccak_syscall

Also passed the linked GPU e2e benchmark run above.

Risks and Rollout

• Soundness risk is concentrated in transcript ordering and verifier frontload evaluation; native and recursion verifiers now follow the same global proof flow.
• Performance is not yet an E2E win in the linked benchmark despite removing per-chip main-constraint cost; further scheduling/host-overlap work is needed before rollout as a performance improvement.

Follow-ups

• Investigate reducing the new prove_batched_main_constraints critical-path cost.
• Keep benchmark summaries explicit that parsed module totals overlap and are not a wall-time decomposition.

Copilot Reviewer Directive (keep this section)

When Copilot reviews this PR, apply .github/copilot-instructions.md strictly.