On Thu, May 23, 2024 at 08:25:17PM +0100, Giuliano Procida wrote: > Hi. > > (edited repost due to unfortunate HTML email). > > Until the reproducible BTF changes land in a new pahole version, and for > anyone stuck on older versions, pahole -J -j typically produces > non-deterministic BTF. > > For Android, we are converging to hermetic, reproducible builds. .BTF > sections are a significant difference we see. I have trivial patches to > pass -j1 instead of -j for the older versions we are using (1.23 and 1.25). > > Trivial patches: > https://android-review.googlesource.com/q/Ibd72ac638faa1826f6655b336cc7001591ea70f1 That should be at least configurable thru a CONFIG_REPRODUCIBLE_BUILD that then would check the pahole version and if less than 1.27 then would use -j1 So it continues to use -j from the version where it was introduced, 1.22, but for people wanting reproducible builds it plain don't use -j or if you really want to be explicit, uses -j1 as you did. For >= 1.27 we will have 'reproducible_build' added to the --btf_features= line if CONFIG_REPRODUCIBLE_BUILD is set. > Gaining determinism for the older versions means giving up some performance. > About a factor of 2.1 in our case (or an extra 10s on vmlinux). > Do others want performance or determinism, should I send patches to LKML > and the stable list? But that is with older paholes, for 1.27, to be released next week, one will just use '--btf_features=+reproducible_build and continue to have parallel DWARF loading with serialized BTF encoding, which should be close to the non-reproducible build numbers. > Off-topic: pahole -J -j9 is faster than -j on my machine with 36 > cores, by another > factor of 2. This is v1.25. -j1 18.7s, -j9 4.5s, -j 8.9s. I'll try to profile that on a 5950X (16 cores, 32 threads) and a 14700K (8 performance cores (16 threads) + 12 efficiency cores (12 threads), total 28 threads) to try and see if I can get a better heuristic that takes into account these factors on the most recent codebase that will become 1.27 next week. - Arnaldo
