RFC: I Shaved 63% Off My Build Time with This One Weird Trick (Developers HATE this!)

[taalojarvi]

Hi @Locietta,

This pull request introduces a set of patches that significantly reduce the execution time of GitHub Actions builds.

Key Improvements:

• Cache implementation: Caches build artifacts using ccache, resulting in a significant speedup by reusing pre-compiled objects.
• SMT awareness in CMake: Accurately accounts for the number of available threads when scheduling jobs, leading to better utilization of runners.
• Separate caches per architecture: Prevents cache poisoning by isolating caches for different architectures.
• Monthly LTS builds: Reduces runner utilization by scheduling LTS builds less frequently.

Results:

• Total duration reduction: Before the patchset, a normal build without SMT awareness and ccache took approximately 30 minutes and 2 seconds. After applying the changes, the build time is reduced to 11 minutes and 42 seconds, representing a 63% improvement. You can see the detailed build run here.

Ccache Statistics:

Cacheable calls: 3359 / 4738 (70.89%) 
Hits: 3353 / 3359 (99.82%) 
Direct: 3353 / 3353 (100.0%) 
Preprocessed: 0 / 3353 ( 0.00%) 
Misses: 6 / 3359 ( 0.18%) 
Uncacheable calls: 1379 / 4738 (29.11%) 

Additional notes:

• Ccache is not used for LTS builds to ensure that we have a clean LTS build.
• This is a sort of thank you from my side for the great work you've put into developing this project.