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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 eca5347d2b
commit a1e6a310ad
1 changed files with 1 additions and 1 deletions
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scripts/Makefile.btf
+1 -1
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@@ -10,7 +10,7 @@ endif
pahole-flags-$(call test-ge, $(pahole-ver), 121) += --btf_gen_floats
pahole-flags-$(call test-ge, $(pahole-ver), 122) += -j
pahole-flags-$(call test-ge, $(pahole-ver), 122) += -j1
pahole-flags-$(CONFIG_PAHOLE_HAS_LANG_EXCLUDE) += --lang_exclude=rust