perf test: Add a perf event fallback test

This adds test cases to verify the precise ip fallback logic:

- If the system supports precise ip, for an event given with the maximum
  precision level, it should be able to decrease precise_ip to find a
  supported level.
- The same fallback behavior should also work in more complex scenarios,
  such as event groups or when PEBS is involved

Additional fallback tests, such as those covering missing feature cases,
can be added in the future.

Suggested-by: Ian Rogers <[email protected]>
Reviewed-by: Dapeng Mi <[email protected]>
Signed-off-by: Zide Chen <[email protected]>
Reviewed-by: Ian Rogers <[email protected]>
Signed-off-by: Namhyung Kim <[email protected]>

tools/perf/tests/shell/test_event_open_fallback.sh

@@ -0,0 +1,86 @@
+#!/bin/bash
+# Perf event open fallback test
+# SPDX-License-Identifier: GPL-2.0
+
+skip_cnt=0
+ok_cnt=0
+err_cnt=0
+
+cleanup()
+{
+	rm -f perf.data
+	rm -f perf.data.old
+	trap - EXIT TERM INT
+}
+
+trap_cleanup()
+{
+	cleanup
+	exit 1
+}
+
+trap trap_cleanup EXIT TERM INT
+
+perf_record()
+{
+	perf record "$@" -- true 1>/dev/null 2>&1
+}
+
+test_decrease_precise_ip()
+{
+	echo "Decrease precise ip test"
+
+	perf list pmu | grep -q 'cycles' || return 2
+
+	if ! perf_record -e cycles; then
+		return 2
+	fi
+
+	# It should reduce precision level down to 0 if needed.
+	if ! perf_record -e cycles:P; then
+		return 1
+	fi
+	return 0
+}
+
+test_decrease_precise_ip_complicated()
+{
+	echo "Decrease precise ip test (complicated case)"
+
+	perf list pmu | grep -q 'mem-loads-aux' || return 2
+
+	if ! perf_record -e '{cpu/mem-loads-aux/S,cpu/mem-loads/PS}'; then
+		return 1
+	fi
+	return 0
+}
+
+count_result()
+{
+	if [ "$1" -eq 2 ] ; then
+		skip_cnt=$((skip_cnt + 1))
+		return
+	fi
+	if [ "$1" -eq 0 ] ; then
+		ok_cnt=$((ok_cnt + 1))
+		return
+	fi
+	err_cnt=$((err_cnt + 1))
+}
+
+ret=0
+test_decrease_precise_ip		|| ret=$? ; count_result $ret ; ret=0
+test_decrease_precise_ip_complicated	|| ret=$? ; count_result $ret ; ret=0
+
+cleanup
+
+if [ ${err_cnt} -gt 0 ] ; then
+	exit 1
+fi
+
+if [ ${ok_cnt} -gt 0 ] ; then
+	exit 0
+fi
+
+# Skip
+exit 2