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

[Ian Rogers <irogers@google.com>]

Replace hardcoded 'make' calls with '$(MAKE)' within tests/make
to ensure GNU Make jobserver file descriptors are properly inherited
by nested builds.

Additionally, remove the notorious 'unexport MAKEFLAGS' from
tools/perf/Makefile. This hack was originally added to prevent
the wrapper's internal '-j$(JOBS)' override from crashing when parent jobserver
tokens were present. Instead, use proper GNU Make conditionals to check
for '-j' or 'jobserver' strings within MAKEFLAGS. If a jobserver is
already orchestrating the build, gracefully back off and let GNU Make
manage parallelism natively.

Finally, optimize the 'out' target (which processes 'run_O' out-of-tree builds)
by stripping sequential bottlenecks like $(call clean) from isolated tmp directories,
and wrapping the target list in a parallel sub-make call.

These combined changes enable 'build-test' out-of-tree targets to
build completely concurrently without severing jobserver tokens.

Unscientifically measured the change lowered the build-test from
around 15 minutes to 10 minutes on a 28 threaded Alderlake CPU. Fixing
the jobserver issues meant the machine remained somewhat usable while
running the test.

Signed-off-by: Ian Rogers <irogers@google.com>
Assisted-by: Antigravity:gemini-3.1-pro
---
 tools/perf/Makefile   | 28 +++++++++++++++++-----------
 tools/perf/tests/make | 14 +++++++-------
 2 files changed, 24 insertions(+), 18 deletions(-)

diff --git a/tools/perf/Makefile b/tools/perf/Makefile
index 5b713837eede..45f641e24fb4 100644
--- a/tools/perf/Makefile
+++ b/tools/perf/Makefile
@@ -14,23 +14,29 @@
 .SUFFIXES:
 
 #
-# We don't want to pass along options like -j:
+# If no parallel build was requested, do a parallel build with multiple jobs,
+# based on the number of CPUs online in this system: 'make -j8' on an 8-CPU
+# system, etc.
 #
-unexport MAKEFLAGS
-
-#
-# Do a parallel build with multiple jobs, based on the number of CPUs online
-# in this system: 'make -j8' on a 8-CPU system, etc.
+# If MAKEFLAGS contains '-j' or 'jobserver', JOBS is intentionally left
+# uninitialized so the native GNU Make jobserver can seamlessly control the
+# parallel bounds of the build.
 #
 # (To override it, run 'make JOBS=1' and similar.)
 #
-ifeq ($(JOBS),)
-  JOBS := $(shell (getconf _NPROCESSORS_ONLN || grep -E -c '^processor|^CPU[0-9]' /proc/cpuinfo) 2>/dev/null)
-  ifeq ($(JOBS),0)
-    JOBS := 1
+ifeq ($(findstring -j,$(MAKEFLAGS)),)
+  ifeq ($(findstring jobserver,$(MAKEFLAGS)),)
+    ifeq ($(JOBS),)
+      JOBS := $(shell (getconf _NPROCESSORS_ONLN || grep -E -c '^processor|^CPU[0-9]' /proc/cpuinfo) 2>/dev/null)
+      ifeq ($(JOBS),0)
+        JOBS := 1
+      endif
+    endif
+    PARALLEL_OPT := -j$(JOBS)
   endif
 endif
 
+
 #
 # Only pass canonical directory names as the output directory:
 #
@@ -62,7 +68,7 @@ define print_msg
 endef
 
 define make
-  @$(MAKE) -f Makefile.perf --no-print-directory -j$(JOBS) O=$(FULL_O) $(SET_DEBUG) $@
+  @$(MAKE) -f Makefile.perf --no-print-directory $(PARALLEL_OPT) O=$(FULL_O) $(SET_DEBUG) $@
 endef
 
 #
diff --git a/tools/perf/tests/make b/tools/perf/tests/make
index d2c2f526e1db..4f14c6b72416 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)
 	@TMP_O=$$(mktemp -d); \
 	TMP_DEST=$$(mktemp -d); \
 	cmd="cd $(PERF) && $(MAKE_F) $($(patsubst %_O,%,$@)) $(PARALLEL_OPT) O=$$TMP_O DESTDIR=$$TMP_DEST"; \
@@ -363,18 +362,18 @@ endif
 make_kernelsrc:
 	@echo "- make -C <kernelsrc> $(PARALLEL_OPT) $(K_O_OPT) tools/perf"
 	$(call clean); \
-	(make -C ../.. $(PARALLEL_OPT) $(K_O_OPT) tools/perf) > $@ 2>&1 && \
+	($(MAKE) -C ../.. $(PARALLEL_OPT) $(K_O_OPT) tools/perf) > $@ 2>&1 && \
 	test -x $(KERNEL_O)/tools/perf/perf && rm -f $@ || (cat $@ ; false)
 
 make_kernelsrc_tools:
 	@echo "- make -C <kernelsrc>/tools $(PARALLEL_OPT) $(K_O_OPT) perf"
 	$(call clean); \
-	(make -C ../../tools $(PARALLEL_OPT) $(K_O_OPT) perf) > $@ 2>&1 && \
+	($(MAKE) -C ../../tools $(PARALLEL_OPT) $(K_O_OPT) perf) > $@ 2>&1 && \
 	test -x $(KERNEL_O)/tools/perf/perf && rm -f $@ || (cat $@ ; false)
 
 make_libperf:
 	@echo "- make -C lib";
-	make -C lib clean >$@ 2>&1; make -C lib >>$@ 2>&1 && rm $@
+	$(MAKE) -C lib clean >$@ 2>&1; $(MAKE) -C lib >>$@ 2>&1 && rm $@
 
 FEATURES_DUMP_FILE := $(FULL_O)/BUILD_TEST_FEATURE_DUMP
 FEATURES_DUMP_FILE_STATIC := $(FULL_O)/BUILD_TEST_FEATURE_DUMP_STATIC
@@ -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)
 	@echo OK
 	@rm -f $(FEATURES_DUMP_FILE) $(FEATURES_DUMP_FILE_STATIC)
 
 ifeq ($(REUSE_FEATURES_DUMP),1)
 $(FEATURES_DUMP_FILE):
 	$(call clean)
-	@cmd="cd $(PERF) && make FEATURE_DUMP_COPY=$@ $(O_OPT) feature-dump"; \
+	@cmd="cd $(PERF) && $(MAKE) FEATURE_DUMP_COPY=$@ $(O_OPT) feature-dump"; \
 	echo "- $@: $$cmd" && echo $$cmd && \
 	( eval $$cmd ) > /dev/null 2>&1
 
 $(FEATURES_DUMP_FILE_STATIC):
 	$(call clean)
-	@cmd="cd $(PERF) && make FEATURE_DUMP_COPY=$@ $(O_OPT) LDFLAGS='-static' feature-dump"; \
+	@cmd="cd $(PERF) && $(MAKE) FEATURE_DUMP_COPY=$@ $(O_OPT) LDFLAGS='-static' feature-dump"; \
 	echo "- $@: $$cmd" && echo $$cmd && \
 	( eval $$cmd ) > /dev/null 2>&1
 
-- 
2.55.0.966.g6673acef38-goog