nixpkgs/ci/eval
Wolfgang Walther af6faf8760
workflows/eval: remove attrs step
Previously, the attrs step consisted of:
- 7s queue time
- 1m 15s run time

Only 25s of this were spent preparing the attr paths. A bit more than a
minute was just spent for queuing, checking out the repo, downloading
nix, downloading dependencies, uploading the artifacts - and then
downloading them again in the next step. All of that can be avoided if
we collect the attrs as part of the outpaths job.

By running the attrs step as part of each outpaths step the attrpaths
will be collected 4x, but:
- We save a minute for each eval run to complete.
- We save a full job, giving us more free runners and *possibly* less
queue times for other jobs in the repo.
- We reduce complexity in the workflow file.
2025-05-11 22:22:48 +02:00
..
compare check-meta: wrap maintainers attribute to include team members (#402991) 2025-05-07 17:11:15 -04:00
default.nix workflows/eval: remove attrs step 2025-05-11 22:22:48 +02:00
README.md workflows/eval: load supportedSystems from JSON file 2025-05-11 22:22:45 +02:00

Nixpkgs CI evaluation

The code in this directory is used by the eval.yml GitHub Actions workflow to evaluate the majority of Nixpkgs for all PRs, effectively making sure that when the development branches are processed by Hydra, no evaluation failures are encountered.

Furthermore it also allows local evaluation using

nix-build ci -A eval.full \
  --max-jobs 4 \
  --cores 2 \
  --arg chunkSize 10000 \
  --arg evalSystems '["x86_64-linux" "aarch64-darwin"]'
  • --max-jobs: The maximum number of derivations to run at the same time. Only each supported system gets a separate derivation, so it doesn't make sense to set this higher than that number.
  • --cores: The number of cores to use for each job. Recommended to set this to the amount of cores on your system divided by --max-jobs.
  • chunkSize: The number of attributes that are evaluated simultaneously on a single core. Lowering this decreases memory usage at the cost of increased evaluation time. If this is too high, there won't be enough chunks to process them in parallel, and will also increase evaluation time.
  • evalSystems: The set of systems for which nixpkgs should be evaluated. Defaults to the four official platforms (x86_64-linux, aarch64-linux, x86_64-darwin and aarch64-darwin).

A good default is to set chunkSize to 10000, which leads to about 3.6GB max memory usage per core, so suitable for fully utilising machines with 4 cores and 16GB memory, 8 cores and 32GB memory or 16 cores and 64GB memory.

Note that 16GB memory is the recommended minimum, while with less than 8GB memory evaluation time suffers greatly.