[RFC/PATCHES 00/12] pahole: Reproducible parallel DWARF loading/serial BTF encoding

[Arnaldo Carvalho de Melo <acme@kernel.org>]

Hi,

	This allows us to have reproducible builds while keeping the
DWARF loading phase in parallel, achieving a noticeable speedup as
showed in the commit log messages:

On a:

  model name    : Intel(R) Core(TM) i7-14700K

  8 performance cores (16 threads), 12 efficiency cores.

Serial encoding:

  $ perf stat -e cycles -r5 pahole --btf_encode_detached=vmlinux.btf.serial vmlinux
             5.18276 +- 0.00952 seconds time elapsed  ( +-  0.18% )

Parallel, but non-reproducible:

  $ perf stat -e cycles -r5 pahole -j --btf_encode_detached=vmlinux.btf.parallel vmlinux
              1.8529 +- 0.0159 seconds time elapsed  ( +-  0.86% )

reproducible build done using parallel DWARF loading + CUs-ordered-as-in-vmlinux serial BTF encoding:

  $ perf stat -e cycles -r5 pahole -j --reproducible_build --btf_encode_detached=vmlinux.btf.parallel.reproducible_build vmlinux
              2.3632 +- 0.0164 seconds time elapsed  ( +-  0.69% )

Please take a look, its in the 'next' branch at:

  https://git.kernel.org/pub/scm/devel/pahole/pahole.git
  https://git.kernel.org/pub/scm/devel/pahole/pahole.git/log/?h=next

There is a new tool to do regression testing on this feature:

  https://git.kernel.org/pub/scm/devel/pahole/pahole.git/commit/?h=next&id=c751214c19bf8591bf8e4abdc677cbadee08f630
  
And here a more detailed set of tests using it:

  https://git.kernel.org/pub/scm/devel/pahole/pahole.git/commit/?h=next&id=4451467ca16a6e31834f6f98661c63587ce556f7

Working on libbpf to allow for parallel reproducible BTF encoding is the
next step.

Thanks a lot,

- Arnaldo

Arnaldo Carvalho de Melo (12):
  core: Allow asking for a reproducible build
  pahole: Disable BTF multithreaded encoded when doing reproducible builds
  dwarf_loader: Separate creating the cu/dcu pair from processing it
  dwarf_loader: Introduce dwarf_cus__process_cu()
  dwarf_loader: Create the cu/dcu pair in dwarf_cus__nextcu()
  dwarf_loader: Remove unused 'thr_data' arg from dwarf_cus__create_and_process_cu()
  core: Add unlocked cus__add() variant
  core: Add cus__remove(), counterpart of cus__add()
  dwarf_loader: Add the cu to the cus list early, remove on LSK_DELETE
  core/dwarf_loader: Add functions to set state of CU processing
  pahole: Encode BTF serially in a reproducible build
  tests: Add a BTF reproducible generation test

 dwarf_loader.c              | 73 +++++++++++++++++++++++---------
 dwarves.c                   | 58 ++++++++++++++++++++++++-
 dwarves.h                   | 17 ++++++++
 pahole.c                    | 84 +++++++++++++++++++++++++++++++++++--
 tests/reproducible_build.sh | 56 +++++++++++++++++++++++++
 5 files changed, 264 insertions(+), 24 deletions(-)
 create mode 100755 tests/reproducible_build.sh

-- 
2.44.0