CI: use more CPUs for building

[SpecLad]

The standard GitHub runners have 3 to 4 CPUs, depending on the OS: https://docs.github.com/en/actions/using-github-hosted-runners/about-github-hosted-runners/about-github-hosted-runners#standard-github-hosted-runners-for-public-repositories. Increase the number of Make jobs to utilize those CPUs better.

[rb6502]

The change itself is reasonable, but my understanding is that there are GitHub-imposed resource limits that we potentially could run into and that's why the settings are low right now.

[SpecLad]

I'm not aware of any additional limits. You get the runner that you get, and it's up to you how to use it.

and that's why the settings are low right now.

I assumed that they are low because they were configured before GitHub started using 4-core runners (which is this year: https://github.blog/2024-01-17-github-hosted-runners-double-the-power-for-open-source/).

[rb6502]

https://docs.mamedev.org/contributing/index.html says we've had contributors banned from GitHub for using "too much" CPU and GitHub would not define what "too much" is. I don't remember the specific details (@cuavas might) but apparently it's a thing.

[plaes]

Proper way to do that would be make -j$(nproc).

[cuavas]

I’d be somewhat concerned about that with limited memory. A -j5 build on a fairly minimal Linux system with 6GB RAM hits swap pretty hard at two points whether you use GCC or clang. The macOS runners only have 7GB RAM, so I wouldn’t want to sail too close to the wind.

[cuavas]

https://docs.mamedev.org/contributing/index.html says we've had contributors banned from GitHub for using "too much" CPU and GitHub would not define what "too much" is. I don't remember the specific details (@cuavas might) but apparently it's a thing.

Correct, @0kmg was banned from GitHub actions.