[not-matthias]

TLDR: Under Valgrind every measured iteration started from a flushed simulated cache, because CALLGRIND_START_INSTRUMENTATION was sent right before it (and it flushes the cache simulator). The harness now switches instrumentation on once before the warmup and only issues ZERO_STATS before the measured iteration, so the measurement sees the cache state the warmup built up (simulation/memory modes only; walltime is untouched).

• CodSpeed::warmup_iteration() drives the warmup for bencher, criterion and divan compat: ≥ WARMUP_MIN_ITERATIONS (1), ≤ WARMUP_MAX_ITERATIONS (5), no new iteration after WARMUP_MAX_DURATION (1 s of simulator time).
• divan compat previously had no warmup at all; iter_manual_unstable now warms up like iter.
• Measured:/Checked: lines append (warmup: N iterations) so analyses can stratify on the count.
• Smoke (callgrind, runner cache geometry, 2 MiB working set, 3 runs each, identical counts across runs): strided_walk DLmr 32769 → 0; sort_clone I1mr/ILmr 11 → 0, DLmr 32770 → 0, D1mw/DLmw 1 → 0. Ir unchanged (+4 for the loop condition).

Review notes

• The dump's summary: line now wraps negative: callgrind derives it from a per-thread baseline that ZERO_STATS only keeps consistent while instrumentation is off. callgrind-parser skips summary: and reads totals:, which is correct under both orders.
• Warmup iterations now run fully instrumented (slower than the previous uninstrumented warmup), bounded by the 1 s cap.
• Stacked on feat(divan): run each benchmark in its own process #194.

Part of COD-3915

[greptile-apps]

Confidence Score: 4/5

[Medium impact] The changes affect benchmark measurements across the Rust compatibility workflows.

The logging requirement must be satisfied before merging; no behavioral blocker was found.

Findings

1.  Warmup output bypasses tracing ▶

Fix with agent prompt

### Issue 1
crates/codspeed/src/codspeed.rs:200-204
The expanded benchmark message uses `println!`, but the repository requires Rust messages to use tracing macros instead of `println!` or `eprintln!`. Move this message to `info!` to satisfy the requirement before merging.

Note: If this suggestion doesn't match your team's coding style, reply to this and let me know. I'll remember it for next time!

---

For each issue above, determine whether it is valid and should be fixed. If so, fix it directly.

Summary

Keeps Callgrind instrumentation running from warmup through measurement so the measured iteration can reuse the warmed simulated cache.

• Measured Rust benchmarks now start with their warmup cache state.
• The compatibility harnesses warm each benchmark before measuring it.
• Benchmark run lines now show how many warmup iterations ran.

not-matthias explicitly acknowledged wrapped summary: values in the PR description and stated that the parser ignores summary: and reads totals:.

Diagram

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A[First warmup request] --> B[Start instrumentation]
    B --> C[Run warmup iteration]
    C --> D{Another warmup allowed?}
    D -->|Yes| C
    D -->|No| E[Zero counters without flushing cache]
    E --> F[Run measured iteration]
    F --> G[Stop instrumentation and dump results]
    G --> H[Report warmup count]

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_{Reviews (1) · Last reviewed commit: "feat(codspeed): run the warmup with the ..." · Reviewed by Greptile}

[greptile-apps]

Warmup output bypasses tracing

The expanded benchmark message uses println!, but the repository requires Rust messages to use tracing macros instead of println! or eprintln!. Move this message to info! to satisfy the requirement before merging.

Rule Used: Never use println!/eprintln! in Rust; use tracing macros (info!/debug!/warn!/error!). (source)

Prompt To Fix With AI

This is a comment left during a code review.
Path: crates/codspeed/src/codspeed.rs
Line: 200-204

Comment:
**Warmup output bypasses tracing**

The expanded benchmark message uses `println!`, but the repository requires Rust messages to use tracing macros instead of `println!` or `eprintln!`. Move this message to `info!` to satisfy the requirement before merging.

**Rule Used:** Never use `println!`/`eprintln!` in Rust; use tracing macros (`info!`/`debug!`/`warn!`/`error!`). ([source](https://app.greptile.com/codspeed/-/custom-context?memory=f04f734b-e556-482b-98b9-64c7ce663663))

---

For each issue above, determine whether it is valid and should be fixed. If so, fix it directly.

Note: If this suggestion doesn't match your team's coding style, reply to this and let me know. I'll remember it for next time!

[codspeed]

Performance comparison unavailable

The base and head of this comparison were measured with different runner settings, so their benchmark values are not directly comparable.

What changed between base and head:

• Cycle estimation (off → on) changes how benchmark performance is calculated. Learn more about cycle estimation

Re-run the base with the same settings to get a valid performance comparison.

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_{Comparing cod-3915-warm-cache-warmup (061f923) with cod-3799-explore-process-per-benchmark-in-codspeed-rust (fce04a6)}