On Mon, May 27, 2024 at 01:49:41PM +0300, Michael Tokarev wrote: > Hi! > > Noticed today that a rebuild of basically the same tree (a few commits apart) > in CI result in just 11% hit rate of ccache: > > https://gitlab.com/mjt0k/qemu/-/jobs/6947445337#L5054 > > while it should be near 100%. What's interesting in there is: > > 1) cache size is close to max cache size, > and more important, > 2) cleanups performed 78 > > so it has to remove old entries before it finished the build. > > So effectively, our ccache usage is an extra burden, not help.
I think this ends up being different per job. If I try the 'build-system-fedora' job, for example, I get a 99% cache hit rate, and 0.2 GB usage of cache storage https://gitlab.com/berrange/qemu/-/jobs/6876054586 $ ccache --show-stats Cacheable calls: 3018 / 3208 (94.08%) Hits: 49 / 3018 ( 1.62%) Direct: 0 / 49 ( 0.00%) Preprocessed: 49 / 49 (100.0%) Misses: 2969 / 3018 (98.38%) Uncacheable calls: 190 / 3208 ( 5.92%) Local storage: Cache size (GB): 0.2 / 0.5 (30.55%) Hits: 49 / 3018 ( 1.62%) Misses: 2969 / 3018 (98.38%) If I compare the jobs, the big differences are the target lists: CentOS: '--target-list=ppc64-softmmu or1k-softmmu s390x-softmmu x86_64-softmmu rx-softmmu sh4-softmmu' Fedora: '--target-list=microblaze-softmmu mips-softmmu xtensa-softmmu m68k-softmmu riscv32-softmmu ppc-softmmu sparc64-softmmu' And then a few minor things: CentOS: '--disable-nettle' '--enable-gcrypt' '--enable-vfio-user-server' '--enable-modules' '--enable-trace-backends=dtrace' Fedora: '--disable-gcrypt' '--enable-nettle' the crypto won't make a diffeernce to caching. Modules ought not to make a difference either, as that's just moving some .o files from the exe to a so, not adding many more exes. The trace backends will add quite a few .o files, but I'm not sure that will impact cache. IOW, I bet the target list has the big difference on the amount of data that needs to be cached, to explain the different cache usage. I wonder what the picture looks like for cache hits / cache disk usage across all the other jobs. Is CentOS an outlier or is FEdora an outlier? We do want cache to be in the 90+% mark if possible as it has a big impact on build time. > I should be increased at least, I think. But it's actually difficult > to say really, - is the cache shared between all builds or is it unique > for each build config? Because if it the former, it shouldn't even > work since different ccache versions use different format of the files > in cache. It is unique per job per buildtest-template.yml: cache: paths: - ccache key: "$CI_JOB_NAME" when: always > What's unique in my pipeline run - I ran just a single build job > in two pipelines, nothing more. In my test I ran a job, then re-ran it in the same pipeline. With regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|
