Use ccache in github actions builds

[scottwittenburg]

Add an action available on the marketplace to GithubActions builds, which simplifies using ccache to speed up compilation. The table below shows the speed up for some of the affected builds (note: times are build times only, and do not include any of the other steps). On the first run, the cache was empty, so there was no benefit at all. On the second run, the cache hit rates were all around 100%, since I didn't change any source files in between.

                  Build Name                  |         Time To Build
                                              |   first run  |  second run
----------------------------------------------|-----------------------------
  linux_ubuntu (ubuntu20.04, gcc8, serial)    |     7m 28s   |      44s
  linux_ubuntu (ubuntu20.04, gcc8, ompi)      |    10m 30s   |   1m 36s
  linux_ubuntu (ubuntu20.04, gcc9, ompi)      |     9m 27s   |   1m 36s
  linux_ubuntu (ubuntu20.04, gcc10, ompi)     |    12m 36s   |   1m 29s
  linux_ubuntu (ubuntu20.04, gcc10, mpich)    |     9m  3s   |   1m 20s
  linux_ubuntu (ubuntu20.04, gcc11, ompi)     |     9m 13s   |   1m 25s
  linux_ubuntu (ubuntu20.04, clang6, serial)  |     4m 38s   |      40s
  linux_ubuntu (ubuntu20.04, clang6, ompi)    |     6m 58s   |   1m 31s
  linux_ubuntu (ubuntu20.04, clang10, ompi)   |     7m 22s   |   1m 20s

I pre-installed ccache in builds where we control the image being used, but ccache-action installs it if it doesn't exist.

As a follow-on, or even in this PR, we could consider using dependabot to keep this action (and any others we use, eg checkout, upload-artifact, etc) up to date. See here.

[scottwittenburg]

Looking at one of the windows builds, I see this issue, where it isn't saving any cache files after the build.

It seems to be a known issue, see here.

[vicentebolea]

Looking at one of the windows builds, I see this issue, where it isn't saving any cache files after the build.

It seems to be a known issue, see here.

If this will halt this feature, we can come back later to add ccache to windows builds.

[vicentebolea]

@scottwittenburg let me know when you need review, I was asked to review automatically since I was listed in the codeowner.

[scottwittenburg]

If this will halt this feature, we can come back later to add ccache to windows builds.

I don't see it halting the feature. We can disable it on windows for now, and as you suggest, come back to it later. Also, as an alternate option, I think we could leave it enabled, even though there's no benefit currently, since the cost is low (based on the times listed in the action log, only a few seconds to install ccache, no time to restore cache, and a second or something to print the message about not saving cache).

Do you have a preference? I can see pros/cons both ways, and am interested in your thoughts.

[vicentebolea]

Do you have a preference?

Disable it in Windows, using ccache we always incur in a overhead, cache miss + build TU is worse than build TU.

[vicentebolea]

Great that this is working! Thanks a lot! lets try to get rid of that gh action since we could replace it by a few env var exports.

[scottwittenburg]

@vicentebolea Please take a look when you get a chance. If you don't have any more suggestions, I will just rewrite the history into two commits, and then we can merge.

[vicentebolea]

@scottwittenburg I just rebased your branch so that it contains the latest commit that "fixes" the tests failures.

[scottwittenburg]

Cache was not saved on any of the runs on master, see here for example.

In my PR testing, I exercised half of this conditional before adding the additional criteria github.ref_name == 'master', by re-running a workflow on the same sha and making sure that cache was not saved.

So I'm not sure yet why it didn't save cache. Here it says that the ${{ }} is not required in if: statements, but then it proceeds to use them everywhere in that documentation anyway. Maybe I need to add those?

[vicentebolea]

}} is

That is odd, I guess that we need to merge it to check it