LLVM: mark as big-parallel

[bennofs]

Motivation for this change

LLVM frequently times out (see https://hydra.nixos.org/job/nixos/release-20.03-aarch64/nixpkgs.llvm_9.aarch64-linux as an example), hopefully marking as big-parallel should give it enough resources to finish quicker. LLVM 5 was already marked as big-parallel, so I went and marked the newer versions big-parallel as well.

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS linux)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Ensured that relevant documentation is up to date
• Fits CONTRIBUTING.md.

[bennofs]

Question: should we only apply big-parallel on aarch64? This might reduce the rebuilt amount?

[bhipple]

With the number of rebuilds, this should go to staging I think.

[bennofs]

Rebased to staging, wasn't sure at first whether a change in requiredSystemFeatures would cause rebuilds.

[FRidh]

Will this have any effect? As far as I know big-parallel is one of the "legacy" features that every Nix installation has on by default. https://github.com/NixOS/nixos-org-configurations/search?q=big-parallel&unscoped_q=big-parallel also doesn't yield anything interesting.

[bennofs]

@FRidh on #nixos-aarch64, @grahamc said:

gchristensen: big-parallel jobs get 32 cores, and 2 jobs per machine, regular builds get 2 cores and 16 jobs per machine

[jonringer]

I think it's largely an infrastructure optimization, as the wiki section on distributed builds mentions it. https://nixos.wiki/wiki/Distributed_build

[vcunat]

❤️ except that llvm 10 is missing. I think it's worth picking to staging-20.03 as well, on the next big rebuild.

[bennofs]

llvm_10 added

[jonringer]

unfortunately, these are all broken currently

[13:44:06] jon@nixos ~/projects/nixpkgs (staging)
$ nix build -f . llvm_{6,7,8,9,10} --keep-going
builder for '/nix/store/ajqw5mrccbf26axn1mcp39l8lmvxgx93-libbfd-2.34.drv' failed with exit code 1; last 10 log lines:
  patching file bfd/configure.ac
  Hunk #1 FAILED at 241.
  1 out of 1 hunk FAILED -- saving rejects to file bfd/configure.ac.rej
  patching file opcodes/Makefile.am
  Hunk #1 succeeded at 51 (offset -1 lines).
  Hunk #2 succeeded at 301 (offset -2 lines).
  Hunk #3 succeeded at 322 (offset -2 lines).
  patching file opcodes/configure.ac
  Hunk #1 succeeded at 86 (offset -3 lines).
  Hunk #2 succeeded at 138 (offset 3 lines).
cannot build derivation '/nix/store/fspqc2gbf618gqaqsfllysh0kkdjxcrg-llvm-10.0.0.drv': 1 dependencies couldn't be built
cannot build derivation '/nix/store/2rd1i67dwg5v380yg8c58y7g44lns19c-llvm-6.0.1.drv': 1 dependencies couldn't be built
cannot build derivation '/nix/store/qvhcq0v99cgjxjq6788ydps3d9gv6lfc-llvm-7.1.0.drv': 1 dependencies couldn't be built
cannot build derivation '/nix/store/5w107rwvi902r1jsbff4b91rh96bzxpa-llvm-8.0.1.drv': 1 dependencies couldn't be built
cannot build derivation '/nix/store/jrwd4z8csc2l70fw92rd374q1vgnfv15-llvm-9.0.1.drv': 1 dependencies couldn't be built
[0 built (1 failed)]
error: build of '/nix/store/2rd1i67dwg5v380yg8c58y7g44lns19c-llvm-6.0.1.drv', '/nix/store/5w107rwvi902r1jsbff4b91rh96bzxpa-llvm-8.0.1.drv', '/nix/store/fspqc2gbf618gqaqsfllysh0kkdjxcrg-llvm-10.0.0.drv', '/nix/store/jrwd4z8csc2l70fw92rd374q1vgnfv15-llvm-9.0.1.drv', '/nix/store/qvhcq0v99cgjxjq6788ydps3d9gv6lfc-llvm-7.1.0.drv' failed

EDIT: fixed by: #86260