ci: add memtrack walltime benchmarks to CI

[not-matthias]

Adds a memtrack-benchmarks CI job that runs codspeed-memtrack track against a few representative workloads (ls, dd, tar), each with RSS-only and RSS+rmap variants, to catch regressions in memtrack's own overhead.

Runs both walltime (execution time) and memory (memtrack's own peak RSS/allocations while tracking each workload) modes against the same crates/memtrack/codspeed.yml config.

[codspeed]

Merging this PR will not alter performance

⚠️ Unknown Walltime execution environment detected

Using the Walltime instrument on standard Hosted Runners will lead to inconsistent data.

For the most accurate results, we recommend using CodSpeed Macro Runners: bare-metal machines fine-tuned for performance measurement consistency.

✅ 17 untouched benchmarks
🆕 12 new benchmarks

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
🆕	WallTime	memtrack track tar	N/A	9.7 s	N/A
🆕	WallTime	memtrack track tar (with physical)	N/A	9.8 s	N/A
🆕	WallTime	memtrack track dd	N/A	1.3 s	N/A
🆕	WallTime	memtrack track dd (with physical)	N/A	1.5 s	N/A
🆕	WallTime	memtrack track ls	N/A	1.2 s	N/A
🆕	WallTime	memtrack track ls (with physical)	N/A	1.2 s	N/A
🆕	Memory	memtrack track tar	N/A	50.5 MB	N/A
🆕	Memory	memtrack track tar (with physical)	N/A	50.9 MB	N/A
🆕	Memory	memtrack track dd	N/A	50.9 MB	N/A
🆕	Memory	memtrack track dd (with physical)	N/A	51.1 MB	N/A
🆕	Memory	memtrack track ls	N/A	50.9 MB	N/A
🆕	Memory	memtrack track ls (with physical)	N/A	51 MB	N/A

---

_{Comparing cod-3093-memtrack-data-format-improvements (ae11946) with main (88c994e)}

[greptile-apps]

Confidence Score: 5/5

The PR appears safe to merge with no outstanding correctness or repository-rule issues.

Summary

This PR adds CI coverage for memtrack overhead and optimizes its event pipeline by sending events in batches.

• Runs RSS-only and physical-memory variants of representative ls, dd, and tar workloads in walltime and memory modes.
• Uses the dedicated codspeed-macro runner for walltime measurements and pins both memtrack and the CodSpeed runner to the tested revision.
• Batches ring-buffer events before channel delivery and updates downstream consumers accordingly.
• Adds regression tests for partial-batch flushing during timeout, explicit drain, and shutdown.
• Adds channel and worker-scaling benchmarks for the event encoder.

Diagram

%%{init: {'theme': 'neutral'}}%%
flowchart LR
    PR[PR revision] --> Matrix{Benchmark mode}
    Matrix -->|walltime| Macro[codspeed-macro]
    Matrix -->|memory| Ubuntu[ubuntu-latest]
    Macro --> Setup[Install and configure memtrack]
    Ubuntu --> Setup
    Setup --> Workloads[Run ls, dd, and tar variants]
    Workloads --> Poller[eBPF ring-buffer poller]
    Poller --> Batch[Batch events]
    Batch --> Encode[Encode memtrack artifacts]
    Encode --> Results[CodSpeed benchmark results]

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_{Reviews (2) · Last reviewed commit: "test(memtrack): bench the channel and wo..."}

[GuillaumeLagrange]

olgtm, good idea!

[GuillaumeLagrange]

Memtrack walltime benchmarks took 19m to run, maybe we can shard something before introducing a 20m delay in the CI pipeline? 😇