CodSpeed v5: Only Your Code, at Its Real Cost

Two things stand between a benchmark and the truth: costs that don't match real hardware, and noise that isn't your code. CodSpeed v5 tackles both. Cycle estimation, now on by default, weights each executed instruction by its measured cost on real CPUs, so a div no longer counts the same as a mov. And the new allocation exclusion removes allocator time from your results entirely. Only your code, at its real cost, with the same single-run determinism.

Cycle estimation, on by default

The simulation estimates the total cycles of a benchmark from three components:

• Executed instruction cycles: each instruction weighted by its real hardware cost, built from measured per-instruction latency and throughput data
• L1 cache misses: data fetched from L2/L3, 10-40 cycles
• Last-level cache misses: data fetched from RAM, 100+ cycles

You keep everything that makes Simulation mode useful: benchmarks run once, on standard CI runners, with deterministic results. The estimate just tracks real hardware much more closely. Learn more in the CPU Simulation docs.

Excluding allocator time

Allocators are one of the most common sources of benchmark variance: their cost depends on the OS, the allocator implementation, and its version. If you are optimizing your own code, that cost is noise. With the new opt-in exclude-allocations feature, CodSpeed tags every allocator frame in the call graph and subtracts its time from the reported value. The flame graph still shows the allocator frames, only the reported number changes.

Enable it with the CLI:

codspeed run --exclude-allocations -- <your bench command>

Or in GitHub Actions:

- uses: CodSpeedHQ/action@v5
  with:
    mode: simulation
    exclude-allocations: true
    run: <your bench command>

Learn more in the allocation exclusion docs.

Consistent wall-time profiles on every OS

The walltime profiler now uses our fork of samply on all operating systems, not just macOS. You get the same high-quality stacks and symbol resolution on Linux as on macOS. If you need the previous behavior, set CODSPEED_WALLTIME_PROFILER=perf.

Upgrading

To upgrade, bump the action in your workflow:

- uses: CodSpeedHQ/action@v5

Or update the CLI:

curl -fsSL https://codspeed.io/install.sh | bash

Since the cycle estimation formula changes what Simulation mode measures, runs made with v5 are not comparable with runs from earlier versions. CodSpeed detects this and marks cross-version comparisons as N/A instead of showing a misleading diff. Your first run on v5 becomes the new baseline.

Full release notes on GitHub.