[llvm-dev] RFC: Using GitHub Actions for CI testing on the release/* branches

[Tom Stellard via llvm-dev]

On 12/12/2019 10:53 AM, Reid Kleckner via llvm-dev wrote:
> I think everyone agrees that LLVM needs better CI, automatic pre-commit testing of various platforms, etc. This is not rocket science, it is standard practice for 2019 software engineering.
> 
> I think my concern is that LLVM could prove to be too big and require too many resources for github's infrastructure. How many patches go into LLVM a day, and how many build and test jobs does GitHub allow users to run concurrently before being throttled?
> 

The key point from John's email is that the GitHub CI resources are easily
accessible for everyone.  So even if we aren't using it as a project for CI,
having working CI definitions available so people can pre-test changes in
their own forks is really valuable.

-Tom

> You may have seen that Christian Kuhnel has been working on a pre-commit testing bot that integrates with Phab:
> https://reviews.llvm.org/p/merge_guards_bot/ 
> https://github.com/google/llvm-premerge-checks/blob/master/docs/user_doc.md
> I hope that ends up being the way forward and suits Tom's original release testing goals.
> 
> On Wed, Dec 11, 2019 at 11:43 PM John Byrd via llvm-dev <llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>> wrote:
> 
>     Please forgive the incorrect threading on this reply to Tom Stellard's RFC.
> 
>     > I would like to start using GitHub Actions[1] for CI testing on the release/*
>     > branches.  As far as I know we don't have any buildbots listening to the
>     > release branches, and I think GitHub Actions are a good way for us to
>     > quickly bring-up some CI jobs there.  
> 
>     Personally, I feel that Tom's proof of concept, is more important than we seem to be giving him credit for.
> 
>     As of this writing, the Github actions system permits all comers, six hours of CPU time per build platform.  Due to this long CPU allotment, AFAIK, Github is one of the few CIs in town that lets anyone build and smoke llvm for free.
> 
>     Consider the workflow of someone who has never worked on llvm before.  They will probably fork the monorepo on Github, in order to fix bugs or add a feature or such.  At the moment they do this, they get a built-in workflow that will sanity-check their builds on several important targets.  Zero braining involved.
> 
>     Giving Joe Programmer a CI system that magically smoke tests llvm, out of the box, after he forks the repo, is a compelling reason to make something like Tom's system a standard part of llvm master.
> 
>     Concerns might be raised that llvm is "preferring" one CI system over another.  Some thoughts about that.  First, because the monorepo's on Github, you'll end up going to github.com <http://github.com> anyway to get your first pull.  Second, nothing about Github actions precludes supporting other CI systems in the future.
> 
>     Thanks for your kind consideration.
> 
>     -- 
>     ---
> 
>     John Byrd
>     Gigantic Software
>     2321 E 4th Street
>     Suite C #429
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>     http://www.giganticsoftware.com
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