nixos/restic: add option maxCpuCores to limit cpu-usage per backup-job

[SebTM]

Description of changes

nixos/restic: add option maxCpuCores to limit cpu-usage per backup-job

Uses go environment-variable "GOMAXPROCS" as suggested in the manual.
https://restic.readthedocs.io/en/latest/047_tuning_backup_parameters.html#cpu-usage

Things done

• Built on platform(s)
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• For non-Linux: Is sandboxing enabled in nix.conf? (See Nix manual)
  • sandbox = relaxed
  • sandbox = true
• Tested, as applicable:
  • NixOS test(s) (look inside nixos/tests)
  • and/or package tests
  • or, for functions and "core" functionality, tests in lib/tests or pkgs/test
  • made sure NixOS tests are linked to the relevant packages
• Tested compilation of all packages that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review rev HEAD". Note: all changes have to be committed, also see nixpkgs-review usage
• Tested basic functionality of all binary files (usually in ./result/bin/)
• 24.11 Release Notes (or backporting 23.11 and 24.05 Release notes)
  • (Package updates) Added a release notes entry if the change is major or breaking
  • (Module updates) Added a release notes entry if the change is significant
  • (Module addition) Added a release notes entry if adding a new NixOS module
• Fits CONTRIBUTING.md.

---

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[dotlambda]

There is no need for this option. Just use rcloneConfig.GOMAXPROCS.

[SebTM]

Thanks for the feedback, I see that this will work - but it's not very intuitive/good UX especially for new users. What about renaming rcloneConfig to environment or Config and keeping infos to specify backend e.g. rcloneConfig or GOMAXPROCS there to limit max cpu cores?

I also tried searching for the environment-variable with language-nix through github (user-configs, https://github.com/search?q=GOMAXPROCS+language%3ANix&type=code) so it might not be popular or do I have another issue if my fan goes crazy while restic is running?

[dotlambda]

What about renaming rcloneConfig to environment

That's probably a good idea. But I'm not sure it's worth a breaking change.

You could add GOMAXPROCS to the example.

[SebTM]

Had another look - we can't use rcloneConfig here - as it uses rcloneAttrToConf:

nixpkgs/nixos/modules/services/backup/restic.nix

Line 315 in 6d0a406

rcloneAttrToConf = v: "RCLONE_CONFIG_" + toUpper (rcloneRemoteName + "_" + v);

which prefixes the environment-variables - so maybe it's still the best option or add customEnvironement option?

I know that I could do systemd.services."restic-backups-${name}".environment but that's more a hack for me.

[nixos-discourse]

This pull request has been mentioned on NixOS Discourse. There might be relevant details there:

https://discourse.nixos.org/t/prs-ready-for-review/1016/147

[SebTM]

@dotlambda ping?

[nixos-discourse]

This pull request has been mentioned on NixOS Discourse. There might be relevant details there:

https://discourse.nixos.org/t/prs-ready-for-review/1016/161

[nixos-discourse]

This pull request has been mentioned on NixOS Discourse. There might be relevant details there:

https://discourse.nixos.org/t/prs-ready-for-review/3032/4265

[SebTM]

Did my best to get feedback/review - will rebase-merge after next week 21/08/2024 - if nobody complains/raises concerns.

[nixos-discourse]

This pull request has been mentioned on NixOS Discourse. There might be relevant details there:

https://discourse.nixos.org/t/prs-ready-for-review/3032/4540