Am 13.02.24 um 18:52 schrieb Julian Sikorski:
Am 13.02.24 um 16:16 schrieb Gary Buhrmaster:
On Tue, Feb 13, 2024 at 9:52 AM Miroslav Suchý <msu...@redhat.com> wrote:

Dne 13. 02. 24 v 9:08 Julian Sikorski napsal(a):
Could this be the reason for ccache not working?

I wonder whether it is Mock problem, Ccache issue or problem in packaging? Does the ccache speadup the build when you
run it with plain rpmbuild and ccache on host?

I have lost track of the details (and the
version of ccache when the issue was
addressed/patched), but ccache at one
time included SOURCE_DATE_EPOCH
in the default hash, resulting in no
cache hits.

This appears to have been fixed in ccache-4.2. F36, obsolete as it is, shipped with 4.5.1.
Having said that, with current kernel there is this line in the log:
+ perl -p -i -e 's/^CONFIG_BUILD_SALT.*/CONFIG_BUILD_SALT="6.7.4-200.lacie03.fc39.x86_64"/' .config
This would change every build.

Best regards,
Julian

I had to bisect a kernel regression once again so I revisited this. I have modified my mock with PR showing ccache stats [1]. Interestingly enough, rebuilding the exact same srpm does result in a significant speedup and almost 100% cache hits. Build took ~12 minutes (as opposed to ~25 when building without cache) and cache stats looks as follows:

DEBUG util.py:463:  Cacheable calls:   21570 / 21954 (98.25%)
DEBUG util.py:463:    Hits:            21554 / 21570 (99.93%)
DEBUG util.py:463:      Direct:        21458 / 21554 (99.55%)
DEBUG util.py:463:      Preprocessed:     96 / 21554 ( 0.45%)
DEBUG util.py:463:    Misses:             16 / 21570 ( 0.07%)
DEBUG util.py:463:  Uncacheable calls:   384 / 21954 ( 1.75%)

Next bisect step, couple hundred commits away (from fe46a7dd189e to eaf0e7a3d271 in case this is relevant), is a completely different story. Build took ~45 minutes and there are almost no cache hits:

DEBUG util.py:463:  Cacheable calls:   21554 / 21938 (98.25%)
DEBUG util.py:463:    Hits:             1421 / 21554 ( 6.59%)
DEBUG util.py:463:      Direct:         1365 /  1421 (96.06%)
DEBUG util.py:463:      Preprocessed:     56 /  1421 ( 3.94%)
DEBUG util.py:463:    Misses:          20133 / 21554 (93.41%)
DEBUG util.py:463:  Uncacheable calls:   384 / 21938 ( 1.75%)

Further down the bisect, despite differences from build to build getting smaller, there is almost no difference. From 902861e34c40 to e5eb28f6d1af, build took around ~45 minutes too, and almost no cache hits were found either:

DEBUG util.py:463:  Cacheable calls:   21571 / 21955 (98.25%)
DEBUG util.py:463:    Hits:             1395 / 21571 ( 6.47%)
DEBUG util.py:463:      Direct:         1373 /  1395 (98.42%)
DEBUG util.py:463:      Preprocessed:     22 /  1395 ( 1.58%)
DEBUG util.py:463:    Misses:          20176 / 21571 (93.53%)
DEBUG util.py:463:  Uncacheable calls:   384 / 21955 ( 1.75%)

Can the cache files be inspected with something to see what is getting cached?

Best regards,
Julian

[1] https://github.com/rpm-software-management/mock/pull/1299
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