Big Endian CI

[dbaileychess]

We should have at least one CI build that uses big endian to test that things don't break in that environment. We usually get external reports (e.g. #7671) when things break.

[dbaileychess]

Wow, twitter actually being useful. This tweet: https://twitter.com/simonw/status/1552703072500977664?lang=en lead me to https://til.simonwillison.net/docker/emulate-s390x-with-qemu

@sunwen18 Do you want to look into trying this out with out CI?

[dbaileychess]

@musicinmybrain FYI

[musicinmybrain]

@musicinmybrain FYI

The Fedora tooling makes it pretty easy do to a local RPM package build for a different architecture using emulation as long as you have qemu-user-static installed:

$ fedpkg --release rawhide mockbuild --root fedora-rawhide-s390x

It’s not fast, by any means, but it works nicely. I do find that occasionally the results of the emulation don’t exactly match those from the real s390x builders, but I don’t have any good examples of this.

In this case, I can build flatbuffers successfully and reproduce #7671 in emulation, which suggests this could be a usable approach for your CI as well.

[sunwen18]

Wow, twitter actually being useful. This tweet: https://twitter.com/simonw/status/1552703072500977664?lang=en lead me to https://til.simonwillison.net/docker/emulate-s390x-with-qemu

@sunwen18 Do you want to look into trying this out with out CI?

Sure, this seems pretty intuitive.

[sunwen18]

So I created a job that can build a ubuntu on s390x architecture in #7707. But one problem with my current set up is that the job takes around 30 minutes. I think it is because everything is running in a docker container. This is really slowing down the CI. So I'm not quite sure about this job.

[musicinmybrain]

I don’t know how long your CI normally takes, but there is a lot of overhead to emulating a different CPU architecture. Expect emulating s390x on x86_64 to take roughly 5–10× as long as running on real hardware.

On my x86_64 machine, a mock-build of the flatbuffers package in Fedora Linux (including installing dependencies, compiling, running the tests, and producing RPMs) takes (real 1m19s / user 5m47s / sys 0m22s). When I emulate s390x it takes (real 9m3s / user 53m20s / sys 0m47s).

[sunwen18]

PR #7707 already merged, I think we can close this issue.