[PATCH v1 2/2] perf test: Add stat metrics --for-each-cgroup test

[Ian Rogers]

Add a new shell test `stat_metrics_cgrp.sh` to verify metric reporting
with `--for-each-cgroup`, both with and without `--bpf-counters`.

The test:
- Checks if system-wide monitoring is supported (skips if not).
- Checks if `insn_per_cycle` metric is supported (skips if not).
- Finds cgroups to test.
- Runs `perf stat` with `insn_per_cycle` metric and verifies that the
  metric is reported for each cgroup and does not contain invalid
  values (like `nan` or `nested`) or empty values when counts are
  present.
- Tests both standard mode and BPF counters mode (if supported).

Assisted-by: Antigravity:gemini-3-flash
Signed-off-by: Ian Rogers <irogers@xxxxxxxxxx>
---
 tools/perf/tests/shell/stat_metrics_cgrp.sh | 123 ++++++++++++++++++++
 1 file changed, 123 insertions(+)
 create mode 100755 tools/perf/tests/shell/stat_metrics_cgrp.sh

diff --git a/tools/perf/tests/shell/stat_metrics_cgrp.sh b/tools/perf/tests/shell/stat_metrics_cgrp.sh
new file mode 100755
index 000000000000..4a29eb9a9067
--- /dev/null
+++ b/tools/perf/tests/shell/stat_metrics_cgrp.sh
@@ -0,0 +1,123 @@
+#!/bin/bash
+# perf stat metrics --for-each-cgroup test
+# SPDX-License-Identifier: GPL-2.0
+
+set -e
+
+test_cgroups=
+
+log_verbose() {
+	echo "$1"
+}
+
+# skip if system-wide is not supported
+check_system_wide()
+{
+	log_verbose "Checking system-wide..."
+	if ! perf stat -a -e instructions sleep 0.01 > /dev/null 2>&1
+	then
+		log_verbose "Skipping: system-wide monitoring not supported"
+		exit 2
+	fi
+}
+
+# find two cgroups to measure
+find_cgroups()
+{
+	log_verbose "Finding cgroups..."
+	# try usual systemd slices first
+	if [ -d /sys/fs/cgroup/system.slice ] && [ -d /sys/fs/cgroup/user.slice ]
+	then
+		test_cgroups="system.slice,user.slice"
+		log_verbose "Found cgroups: ${test_cgroups}"
+		return
+	fi
+
+	# try root and self cgroups
+	find_cgroups_self_cgrp=$(grep perf_event /proc/self/cgroup | cut -d: -f3)
+	if [ -z ${find_cgroups_self_cgrp} ]
+	then
+		# cgroup v2 doesn't specify perf_event
+		find_cgroups_self_cgrp=$(grep ^0: /proc/self/cgroup | cut -d: -f3)
+	fi
+
+	if [ -z ${find_cgroups_self_cgrp} ]
+	then
+		test_cgroups="/"
+	else
+		test_cgroups="/,${find_cgroups_self_cgrp}"
+	fi
+	log_verbose "Found cgroups: ${test_cgroups}"
+}
+
+# Check if metric is reported for each cgroup
+# $1: extra options (e.g. --bpf-counters)
+check_metric_reported()
+{
+	local opts="$1"
+	local output
+
+	log_verbose "Running check_metric_reported with opts '${opts}'..."
+	# Run perf stat
+	if ! output=$(perf stat -a ${opts} \
+			--metrics=insn_per_cycle \
+			--for-each-cgroup ${test_cgroups} \
+			-x, sleep 0.1 2>&1)
+	then
+		echo "FAIL: perf stat failed with exit code $?"
+		echo "Output: ${output}"
+		exit 1
+	fi
+
+	log_verbose "perf stat output:"
+	log_verbose "${output}"
+
+	# Split test_cgroups by comma
+	IFS=',' read -r -a cgrps <<< "${test_cgroups}"
+
+	for cgrp in "${cgrps[@]}"; do
+		# Find lines for this cgroup and metric
+		local cgrp_lines
+		cgrp_lines=$(echo "${output}" | grep "${cgrp}" | grep "insn_per_cycle" || true)
+
+		if [ -z "${cgrp_lines}" ]
+		then
+			echo "FAIL: No metric lines found for cgroup '${cgrp}'"
+			exit 1
+		fi
+
+		# Check for nan or nested
+		if echo "${cgrp_lines}" | grep -q -i -E ",nan,|,nested,"
+		then
+			echo "FAIL: Invalid metric value (nan/nested) for cgroup '${cgrp}'"
+			echo "Line: ${cgrp_lines}"
+			exit 1
+		fi
+		# Check for empty metric value
+		if echo "${cgrp_lines}" | grep -q -E ",,[[:space:]]*[^,]*insn_per_cycle"
+		then
+			echo "FAIL: Empty metric value for cgroup '${cgrp}'"
+			echo "Line: ${cgrp_lines}"
+			exit 1
+		fi
+	done
+	log_verbose "check_metric_reported passed for opts '${opts}'"
+}
+
+check_system_wide
+find_cgroups
+
+# Test 1: Without BPF counters
+check_metric_reported ""
+
+# Test 2: With BPF counters (if supported)
+log_verbose "Checking BPF support..."
+if perf stat -a --bpf-counters --for-each-cgroup / true > /dev/null 2>&1
+then
+	log_verbose "BPF supported, running Test 2..."
+	check_metric_reported "--bpf-counters"
+else
+	log_verbose "BPF not supported, skipping Test 2"
+fi
+
+exit 0
-- 
2.54.0.631.ge1b05301d1-goog