Re: [PATCH v1] perf tests: Improvements to build-test performance

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 2 potential issue(s) to consider:
- [High] The `out` target explicitly passes `-j$(cores)` to a sub-make, breaking GNU Make's native jobserver inheritance and triggering an unbounded fork bomb if `cores` is undefined.
- [Medium] Removing `$(call clean)` from `$(run_O)` causes out-of-tree builds to execute on a dirty source tree when run sequentially after in-tree builds.
--

commit 169a507e0cde997201a5b5a2dfdbe4652f1a9fa0
Author: Ian Rogers <irogers@google.com>

perf tests: Improvements to build-test performance

This commit aims to improve build-test performance by using $(MAKE) to ensure
GNU Make jobserver file descriptors are inherited by nested builds. It removes
sequential bottlenecks like $(call clean) from isolated tmp directories and
wraps the out target list in a parallel sub-make call.

> diff --git a/tools/perf/tests/make b/tools/perf/tests/make
> index d2c2f526e1db0..4f14c6b72416a 100644
> --- a/tools/perf/tests/make
> +++ b/tools/perf/tests/make
> @@ -339,7 +339,6 @@ make_static:
>  	rm -rf $@ $$TMP_DEST || (cat $@ ; false)
>  
>  $(run_O):
> -	$(call clean)

[Severity: Medium]
Does removing this clean step cause out-of-tree builds to execute on a dirty
source tree when run sequentially?

When the default all target is executed:

all: $(run) $(run_O) tarpkg make_kernelsrc make_kernelsrc_tools

The $(run) in-tree builds execute first and leave the source tree dirty.
Since $(run_O) no longer calls $(call clean) before starting, it appears
the first out-of-tree build begins on that dirty source tree, breaking
build isolation.

>  	@TMP_O=$$(mktemp -d); \
>  	TMP_DEST=$$(mktemp -d); \
>  	cmd="cd $(PERF) && $(MAKE_F) $($(patsubst %_O,%,$@)) $(PARALLEL_OPT) O=$$TMP_O DESTDIR=$$TMP_DEST"; \

[ ... ]

> @@ -383,20 +382,21 @@ all: $(run) $(run_O) tarpkg make_kernelsrc make_kernelsrc_tools
>  	@echo OK
>  	@rm -f $(FEATURES_DUMP_FILE) $(FEATURES_DUMP_FILE_STATIC)
>  
> -out: $(run_O)
> +out: $(FEATURES_DUMP_FILE) $(FEATURES_DUMP_FILE_STATIC)
> +	@$(MAKE) -f tests/make $(run_O) PARALLEL_OPT= -j$(cores)

[Severity: High]
Does passing -j$(cores) here break native jobserver inheritance and risk an
unbounded fork bomb?

If a developer runs the out target directly without setting cores, the
-j$(cores) flag expands to -j without an integer. This instructs GNU Make
to spawn unlimited jobs, which is then inherited by all $(run_O) sub-makes.

Additionally, even when cores is defined, passing it explicitly to $(MAKE)
overrides any --jobserver-auth tokens passed from a parent make, breaking
the jobserver inheritance this patch aims to fix.

>  	@echo OK
>  	@rm -f $(FEATURES_DUMP_FILE) $(FEATURES_DUMP_FILE_STATIC)

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260902153135.2067365-1-irogers@google.com?part=1