In pmu-events/Build, ZENS, ARMS, and INTELS were assigned using recursive
assignment (=), and model_name/vendor_name were evaluated using shell
macros (echo ... | sed ...).

Because these variables were expanded inside the COPY_RULE dependency
evaluation loop across hundreds of PMU JSON files and inside every metric
generation recipe, Kbuild continuously re-executed 'ls', 'grep', and 'sed'
shell forks thousands of times during AST parsing and execution.

Convert ZENS, ARMS, and INTELS to simply expanded variables (:=) and replace
model_name/vendor_name with pure GNU Make string functions. This guarantees
Make executes directory probing shell forks exactly once when the Build file
is parsed and evaluates path macros purely in memory, completely eliminating
over 7,800 redundant sub-processes during build startup.

Assisted-by: Gemini:gemini-3.1-pro-preview
Signed-off-by: Ian Rogers <irogers@google.com>
---
 tools/perf/pmu-events/Build | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/tools/perf/pmu-events/Build b/tools/perf/pmu-events/Build
index e957aa2fcb48..246b04f73ccf 100644
--- a/tools/perf/pmu-events/Build
+++ b/tools/perf/pmu-events/Build
@@ -56,12 +56,12 @@ $(LEGACY_CACHE_JSON): $(LEGACY_CACHE_PY)
 # Python to generate architectural metrics
 GEN_METRIC_DEPS := pmu-events/metric.py pmu-events/common_metrics.py
 # Functions to extract the model from an extra-metrics.json or extra-metricgroups.json path.
-model_name = $(shell echo $(1)|sed -e 's@.\+/\(.*\)/extra-metric.*\.json@\1@')
-vendor_name = $(shell echo $(1)|sed -e 's@.\+/\(.*\)/[^/]*/extra-metric.*\.json@\1@')
+model_name = $(notdir $(patsubst %/,%,$(dir $(1))))
+vendor_name = $(notdir $(patsubst %/,%,$(dir $(patsubst %/,%,$(dir $(1))))))
 
 ifeq ($(JEVENTS_ARCH),$(filter $(JEVENTS_ARCH),x86 all))
 # Generate AMD Json
-ZENS = $(shell ls -d pmu-events/arch/x86/amdzen*)
+ZENS := $(shell ls -d pmu-events/arch/x86/amdzen*)
 ZEN_METRICS = $(foreach x,$(ZENS),$(OUTPUT)$(x)/extra-metrics.json)
 ZEN_METRICGROUPS = $(foreach x,$(ZENS),$(OUTPUT)$(x)/extra-metricgroups.json)
 GEN_JSON += $(ZEN_METRICS) $(ZEN_METRICGROUPS)
@@ -78,7 +78,7 @@ endif
 
 ifeq ($(JEVENTS_ARCH),$(filter $(JEVENTS_ARCH),arm64 all))
 # Generate ARM Json
-ARMS = $(shell ls -d pmu-events/arch/arm64/arm/*|grep -v cmn)
+ARMS := $(shell ls -d pmu-events/arch/arm64/arm/*|grep -v cmn)
 ARM_METRICS = $(foreach x,$(ARMS),$(OUTPUT)$(x)/extra-metrics.json)
 ARM_METRICGROUPS = $(foreach x,$(ARMS),$(OUTPUT)$(x)/extra-metricgroups.json)
 GEN_JSON += $(ARM_METRICS) $(ARM_METRICGROUPS)
@@ -95,7 +95,7 @@ endif
 
 ifeq ($(JEVENTS_ARCH),$(filter $(JEVENTS_ARCH),x86 all))
 # Generate Intel Json
-INTELS = $(shell ls -d pmu-events/arch/x86/*|grep -v amdzen|grep -v mapfile.csv)
+INTELS := $(shell ls -d pmu-events/arch/x86/*|grep -v amdzen|grep -v mapfile.csv)
 INTEL_METRICS = $(foreach x,$(INTELS),$(OUTPUT)$(x)/extra-metrics.json)
 INTEL_METRICGROUPS = $(foreach x,$(INTELS),$(OUTPUT)$(x)/extra-metricgroups.json)
 GEN_JSON += $(INTEL_METRICS) $(INTEL_METRICGROUPS)
-- 
2.54.0.563.g4f69b47b94-goog