5.4.0 - 2026-10-02

Release Notes

This release adds a new --experimental-disable-pythonmalloc-override flag to prevent overriding the python allocator, which can cause issues when running free-threaded Python in Simulation mode.

We have also improved the Memory instrument:

• Improved serialization performance for large memory benchmarks
• Physical Memory tracking is now enabled by default (previously opt-in)
• Added support for flamegraphs (enabled by default)

CodSpeed now also works on non-Ubuntu/Debian distributions such as Arch Linux.

🚀 Features

• Expose the run id as a GitHub Actions step output (#551) by @moha-bekh in #551
• Enable rss tracking and memory flamegraphs by default by @not-matthias
• Log process stops and count them per reason by @not-matthias in #543
• Pause producers under ring pressure by @not-matthias
• Add experimental flag to capture allocation stacks by @not-matthias in #522
• Write memtrack module artifacts and metadata by @not-matthias
• Record mapped modules for offline stack attribution by @not-matthias
• Add MemtrackMetadata sharing ModuleArtifacts with walltime by @not-matthias
• Enable stack capture through the tracker by @not-matthias
• Add userspace stack-capture module by @not-matthias
• Capture allocation stacks in eBPF by @not-matthias
• Add agent-plugins manifest and MCP config by @art049
• Add Python allocator opt-out by @not-matthias in #539

🐛 Bug Fixes

• Error out when profile archive exceeds upload size limit (#557) by @lvaroqui in #557
• Honor falsey values of the deprecated memory flags by @not-matthias in #553
• Never resume a reused pid by @not-matthias
• Keep stack hashing scratch inside the ring record by @not-matthias
• Count stack-ring overflow as dropped events by @not-matthias
• Detach BPF links through forked fd holders by @not-matthias
• Read tracking_enabled from a global instead of an array map by @not-matthias
• Skip allocator symbols aliased at an attached offset by @not-matthias
• Honor deprecated experimental flags instead of ignoring them by @not-matthias in #532
• Detect free-threaded Python from venv and uv before setting PYTHONMALLOC by @not-matthias
• Support distributions CodSpeed publishes no valgrind package for (Arch, rolling releases) (#525) by @moha-bekh in #525

🏗️ Refactor

• Drop stack_hash from Free events by @not-matthias in #558
• Inline pid-key deserializer into metadata by @not-matthias
• Capture module mappings with perf by @not-matthias
• Move ELF artifact pipeline to executor/shared by @not-matthias
• Share the yes/no confirmation between the setup steps (#542) by @moha-bekh in #542

📚 Documentation

• Describe the mapping recorder by @not-matthias
• Link the readme logo to codspeed.io by @adriencaccia

⚡ Performance

• Buffer the decompressed memtrack event stream by @not-matthias in #560
• Warm up tar for several complete rounds by @not-matthias in #555
• Drop the teardown-dominated ls benchmark by @not-matthias
• Stop capturing stacks on free by @not-matthias
• Serialize memtrack frames into a buffer and compress in one shot by @codspeedbot
• Stream memtrack encoder frames instead of windows by @not-matthias
• Poll ring buffers every 1ms by @not-matthias
• Resolve stack fp chains off the ring poll thread by @not-matthias
• Switch to mimalloc to reduce memory usage and fragmentation by @not-matthias
• Pre-size the frame output buffer by @not-matthias
• Batch ring-buffer events over the channel by @not-matthias

🧪 Testing

• Ignore duplicate frees in cross-variant comparison by @not-matthias
• Measure ring-pressure pause under an allocation storm by @not-matthias
• Assert nested stack identities by @not-matthias
• Add nested allocation fixtures by @not-matthias
• Cover allocation stack capture by @not-matthias

⚙️ Internals

• Pin memtrack 1.6.0 (#561) by @adriencaccia in #561
• Run the clang-format hook serially by @codspeedbot in #548
• Benchmark runner-shared in memory mode by @not-matthias
• Bump samply-codspeed by @not-matthias in #550
• Cache runner builds across memtrack benchmark shards by @not-matthias in #537
• Add memtrack walltime benchmarks to CI by @not-matthias

Install codspeed-runner 5.4.0

Install prebuilt binaries via shell script

curl --proto '=https' --tlsv1.2 -LsSf https://github.com/CodSpeedHQ/codspeed/releases/download/v5.4.0/codspeed-runner-installer.sh | sh

Download codspeed-runner 5.4.0

File	Platform	Checksum
codspeed-runner-aarch64-apple-darwin.tar.gz	Apple Silicon macOS	checksum
codspeed-runner-aarch64-unknown-linux-musl.tar.gz	ARM64 MUSL Linux	checksum
codspeed-runner-x86_64-unknown-linux-musl.tar.gz	x64 MUSL Linux	checksum