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

Arnaldo Carvalho de Melo
2024-04-02T19:39:55Z

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

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2.44.0