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

[John Byrd via llvm-dev]

> 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?

Please, no one confuse "what should be LLVM's official CIs" with "what can
we do to make it easier for individuals and small companies to experiment
with small changes in their own forks."

Current usage limits for the free Github actions tier are:

- You can execute up to 20 workflows concurrently per repository.
- You can execute up to 1000 API requests in an hour across all actions
within a repository.
- Each job in a workflow can run for up to 6 hours of execution time.
- The number of jobs you can run concurrently across all repositories in
your account depends on your GitHub plan.
- You can have a maximum concurrent set of 5 maximum concurrent MacOS jobs.

So, this isn't enough juice to replace all the LLVM buildbots, but it is
enough to have CI on *your personal fork* of LLVM.  And having CI on
everyone's personal fork, makes it that much more likely that your
Phabricator patches will be correct the first time.

Best of all, if you don't like Github's CI, you can completely ignore it
and proceed with your current workflow.

On Thu, Dec 12, 2019 at 10:53 AM Reid Kleckner <rnk at google.com> 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?
>
> 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> 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 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
>> Santa Ana, CA  92705-3862
>> http://www.giganticsoftware.com
>> T: (949) 892-3526 F: (206) 309-0850
>> _______________________________________________
>> LLVM Developers mailing list
>> llvm-dev at lists.llvm.org
>> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>
>

-- 
---

John Byrd
Gigantic Software
2321 E 4th Street
Suite C #429
Santa Ana, CA  92705-3862
http://www.giganticsoftware.com
T: (949) 892-3526 F: (206) 309-0850
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