Re: [PATCH 1/1] ci: avoid unnecessary builds

["Ævar Arnfjörð Bjarmason" <avarab@gmail.com>]

On Tue, Nov 08 2022, Taylor Blau wrote:

> Whenever a branch is pushed to a repository which has GitHub Actions
> enabled, a bunch of new workflow runs are started.
>
> We sometimes see contributors push multiple branch updates in rapid
> succession, which in conjunction with the impressive time swallowed by
> even just a single CI build frequently leads to many queued-up runs.
>
> This is particularly problematic in the case of Pull Requests where a
> single contributor can easily (inadvertently) prevent timely builds for
> other contributors when using a shared repository.
>
> To help with this situation, let's use the `concurrency` feature of
> GitHub workflows, essentially canceling GitHub workflow runs that are
> obsoleted by more recent runs:
>
>   https://docs.github.com/en/actions/using-workflows/workflow-syntax-for-github-actions#concurrency
>
> For workflows that *do* want the behavior in the pre-image of this
> patch, they can use the ci-config feature to disable the new behavior by
> adding an executable script on the ci-config branch called
> 'skip-concurrent' which terminates with a non-zero exit code.

First, thanks for hacking this up. I've tested this just now in my fork,
and it seems to mostly work as advertised to me, more on the "mostly"
later.

I.e. the "cancel-in-progress" seems to work perfectly. I pushed a branch
with this, it started CI, then I made a trivial update, re-pushed, and
the initial branch's CI run was stopped, one job at a time (not all at
the same time, but almost).

Now, obviously it's a bit more of a verbose solution v.s. Johannes's
original in [1], but on the other hand our main.yml is full of that sort
of copy/pasting already.

Aside from the change under discussion I don't find that to be a big
deal. It's a general "problem", and we could always generate the file
with a script if we really cared, but I think for the forseeable future
the copy/pasting is fine.

But now on the "mostly": I *also* observed that when I turned this off
(I manually patched it to be "skip_concurrent=no" by default) the
"re-push" wouldn't run anything yet, because it was waiting on the other
run. A little "clock" icon is shown, and clicking on the job shows e.g.:

	 Waiting: This workflow is waiting on sparse to complete before running. 

The "sparse" is then a link to the in-progress "sparse" run in the
"other job".

So, completely aside from any catering to my (or anyone else's[2]?)
existing workflow around re-pushes (which I'll freely admit may or may
not be worth the effort), I think this change also has the presumably
unintended effect of changing how CI jobs are queued.

Which is that our workers were before scheduled per-repo (I think), and
you have a finite amount, but they're assigned generally (just from my
observation) in FIFO order based on the jobs that need to be run.

But now you have a queue that'll be piled up on the "repo/workflow/ref"
key. So that e.g. if you have 10 outstanding runs, 10 workers, and all
the pushes have finished except for their "linux-asan" job (or whatever
the slowest one happens to be) that you're only going to run one of
those "linux-asan" jobs at a time.

Now, I think this only matters *if* you flip the "cancel-in-progress" to
"false", so it was a moot point in the original [1]. I.e. you wouldn't
get concurrency anyway, so it didn't matter how things were queued.

This seems pretty clear from the API docs:

	Use concurrency to ensure that only a single job or workflow
	using the same concurrency group will run at a time.

I'm less sure about GitHub, but in other CI systems (e.g. GitLab's) a
"concurrency" feature like that is mainly targeted at jobs that
e.g. need some external resource (say a RDBMS), so you really want that
kind of throttling.

I don't know if there's a workaround for that, I'd think it would be the
logical equivalent of e.g.:

	group: sparse-${{ matrix.nr }}-${{ github.ref }}-${{ needs.ci-config.outputs.skip_concurrent ? github.run_id : "" }}

But the docs say "The expression can only use the github context."[3],
and I don't know if such a thing would fit inside the syntax...


1. https://lore.kernel.org/git/pull.1404.git.1667482458622.gitgitgadget@gmail.com/
2. https://lore.kernel.org/git/75ono097-16nr-nno4-rqoq-rrn79spps249@tzk.qr/
3. https://docs.github.com/en/actions/using-workflows/workflow-syntax-for-github-actions#concurrency


> diff --git a/.github/workflows/check-whitespace.yml b/.github/workflows/check-whitespace.yml
> index ad3466ad16..0bcc9cffbd 100644
> --- a/.github/workflows/check-whitespace.yml
> +++ b/.github/workflows/check-whitespace.yml
> @@ -9,6 +9,12 @@ on:
>    pull_request:
>      types: [opened, synchronize]
>  
> +# Avoid unnecessary builds. Unlike the main CI jobs, these are not
> +# ci-configurable (but could be).
> +concurrency:
> +  group: ${{ github.workflow }}-${{ github.ref }}
> +  cancel-in-progress: true
> +
>  jobs:
>    check-whitespace:
>      runs-on: ubuntu-latest
> diff --git a/.github/workflows/l10n.yml b/.github/workflows/l10n.yml
> index 27f72f0ff3..51fd46e6af 100644
> --- a/.github/workflows/l10n.yml
> +++ b/.github/workflows/l10n.yml
> @@ -2,6 +2,12 @@ name: git-l10n
>  
>  on: [push, pull_request_target]
>  
> +# Avoid unnecessary builds. Unlike the main CI jobs, these are not
> +# ci-configurable (but could be).
> +concurrency:
> +  group: ${{ github.workflow }}-${{ github.ref }}
> +  cancel-in-progress: true
> +
>  jobs:
>    git-po-helper:
>      if: >-
> diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
> index bd6f75b8e0..d27cd44584 100644
> --- a/.github/workflows/main.yml
> +++ b/.github/workflows/main.yml
> @@ -11,6 +11,7 @@ jobs:
>      runs-on: ubuntu-latest
>      outputs:
>        enabled: ${{ steps.check-ref.outputs.enabled }}${{ steps.skip-if-redundant.outputs.enabled }}
> +      skip_concurrent: ${{ steps.check-ref.outputs.skip_concurrent }}
>      steps:
>        - name: try to clone ci-config branch
>          run: |
> @@ -34,7 +35,15 @@ jobs:
>            then
>              enabled=no
>            fi
> +
> +          skip_concurrent=yes
> +          if test -x config-repo/ci/config/skip-concurrent &&
> +             ! config-repo/ci/config/skip-concurrent '${{ github.ref }}'
> +          then
> +            skip_concurrent=no
> +          fi
>            echo "::set-output name=enabled::$enabled"
> +          echo "::set-output name=skip_concurrent::$skip_concurrent"
>        - name: skip if the commit or tree was already tested
>          id: skip-if-redundant
>          uses: actions/github-script@v3
> @@ -82,6 +91,9 @@ jobs:
>      needs: ci-config
>      if: needs.ci-config.outputs.enabled == 'yes'
>      runs-on: windows-latest
> +    concurrency:
> +      group: windows-build-${{ github.ref }}
> +      cancel-in-progress: ${{ needs.ci-config.outputs.skip_concurrent == 'yes' }}
>      steps:
>      - uses: actions/checkout@v2
>      - uses: git-for-windows/setup-git-for-windows-sdk@v1
> @@ -101,11 +113,14 @@ jobs:
>    windows-test:
>      name: win test
>      runs-on: windows-latest
> -    needs: [windows-build]
> +    needs: [ci-config, windows-build]
>      strategy:
>        fail-fast: false
>        matrix:
>          nr: [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
> +    concurrency:
> +      group: windows-test-${{ matrix.nr }}-${{ github.ref }}
> +      cancel-in-progress: ${{ needs.ci-config.outputs.skip_concurrent == 'yes' }}
>      steps:
>      - name: download tracked files and build artifacts
>        uses: actions/download-artifact@v2
> @@ -137,6 +152,9 @@ jobs:
>        NO_PERL: 1
>        GIT_CONFIG_PARAMETERS: "'user.name=CI' 'user.email=ci@git'"
>      runs-on: windows-latest
> +    concurrency:
> +      group: vs-build-${{ github.ref }}
> +      cancel-in-progress: ${{ needs.ci-config.outputs.skip_concurrent == 'yes' }}
>      steps:
>      - uses: actions/checkout@v2
>      - uses: git-for-windows/setup-git-for-windows-sdk@v1
> @@ -184,11 +202,14 @@ jobs:
>    vs-test:
>      name: win+VS test
>      runs-on: windows-latest
> -    needs: vs-build
> +    needs: [ci-config, vs-build]
>      strategy:
>        fail-fast: false
>        matrix:
>          nr: [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
> +    concurrency:
> +      group: vs-test-${{ matrix.nr }}-${{ github.ref }}
> +      cancel-in-progress: ${{ needs.ci-config.outputs.skip_concurrent == 'yes' }}
>      steps:
>      - uses: git-for-windows/setup-git-for-windows-sdk@v1
>      - name: download tracked files and build artifacts
> @@ -218,6 +239,9 @@ jobs:
>      name: ${{matrix.vector.jobname}} (${{matrix.vector.pool}})
>      needs: ci-config
>      if: needs.ci-config.outputs.enabled == 'yes'
> +    concurrency:
> +      group: ${{ matrix.vector.jobname }}-${{ matrix.vector.pool }}-${{ github.ref }}
> +      cancel-in-progress: ${{ needs.ci-config.outputs.skip_concurrent == 'yes' }}
>      strategy:
>        fail-fast: false
>        matrix:
> @@ -281,6 +305,9 @@ jobs:
>      name: ${{matrix.vector.jobname}} (${{matrix.vector.image}})
>      needs: ci-config
>      if: needs.ci-config.outputs.enabled == 'yes'
> +    concurrency:
> +      group: dockerized-${{ matrix.vector.jobname }}-${{ matrix.vector.image }}-${{ github.ref }}
> +      cancel-in-progress: ${{ needs.ci-config.outputs.skip_concurrent == 'yes' }}
>      strategy:
>        fail-fast: false
>        matrix:
> @@ -316,6 +343,9 @@ jobs:
>      env:
>        jobname: StaticAnalysis
>      runs-on: ubuntu-22.04
> +    concurrency:
> +      group: static-analysis-${{ github.ref }}
> +      cancel-in-progress: ${{ needs.ci-config.outputs.skip_concurrent == 'yes' }}
>      steps:
>      - uses: actions/checkout@v2
>      - run: ci/install-dependencies.sh
> @@ -327,6 +357,9 @@ jobs:
>      env:
>        jobname: sparse
>      runs-on: ubuntu-20.04
> +    concurrency:
> +      group: sparse-${{ github.ref }}
> +      cancel-in-progress: ${{ needs.ci-config.outputs.skip_concurrent == 'yes' }}
>      steps:
>      - name: Download a current `sparse` package
>        # Ubuntu's `sparse` version is too old for us
> @@ -345,6 +378,9 @@ jobs:
>      name: documentation
>      needs: ci-config
>      if: needs.ci-config.outputs.enabled == 'yes'
> +    concurrency:
> +      group: documentation-${{ github.ref }}
> +      cancel-in-progress: ${{ needs.ci-config.outputs.skip_concurrent == 'yes' }}
>      env:
>        jobname: Documentation
>      runs-on: ubuntu-latest