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ANDROID: pahole -J -j1 for reproducible BTF

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Versions of pahole from 1.22 support multi-threaded operation with
separate CUs being processed independently. This results in
non-deterministic and effectively non-reproducible output for kernel
objects. Later versions of pahole aim to support determinism by
retiring CUs in order.

We regain determinism by restricting parallelism to 1 at the cost of
some performance.

The default parallelism of `pahole -J` is the number of online
processors * 1.1. Experiments on a workstation with 36 cores reveal
that performance is actually worse for `vmlinux` at `-j` (8.9s) than
at `-j3` (7.8s) and the optimum is around `-j9` (4.9s). No parallelism
is slowest (18.8s), but still acceptable for GKI.

Bug: 342094847
Change-Id: Ibd72ac638faa1826f6655b336cc7001591ea70f1
Signed-off-by: Giuliano Procida <gprocida@google.com>
This commit is contained in:
Giuliano Procida 2024-05-23 09:47:16 +01:00
parent 68c821783c
commit 47a00e599b
1 changed files with 1 additions and 1 deletions
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2
scripts/pahole-flags.sh
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@ -17,7 +17,7 @@ if [ "${pahole_ver}" -ge "121" ]; then
extra_paholeopt="${extra_paholeopt} --btf_gen_floats"
fi
if [ "${pahole_ver}" -ge "122" ]; then
extra_paholeopt="${extra_paholeopt} -j"
extra_paholeopt="${extra_paholeopt} -j1"
fi
if [ "${pahole_ver}" -ge "124" ]; then
# see PAHOLE_HAS_LANG_EXCLUDE