perf python: Add counting.py as example for counting perf events

Add counting.py - a python version of counting.c to demonstrate
measuring and reading of counts for given perf events.

Committer testing:

Build perf and make the generated python binding somewhere you can point
to to avoid using the one in the distro python3-perf (fedora, may be
different in other distros):

$ make -k O=/tmp/build/$(basename $PWD)/ -C tools/perf install-bin

Copy /tmp/build/perf-tools-next/python/perf.cpython-313-x86_64-linux-gnu.so to
somewhere outside this toolbox container and then use it with root:

# export PYTHONPATH=/root/python/
# ls -la /root/python/
total 10640
drwxr-xr-x. 1 root root 72 May 21 11:40 .
dr-xr-x---. 1 root root 574 May 21 11:40 ..
-rwxr-xr-x. 1 acme acme 10894360 May 21 11:40 perf.cpython-313-x86_64-linux-gnu.so
# tools/perf/python/counting.py | head -5
For evsel(software/cpu-clock/) val: 2930946 enable: 2932479 run: 2932479
For evsel(software/cpu-clock/) val: 2924975 enable: 2926267 run: 2926267
For evsel(software/cpu-clock/) val: 2921017 enable: 2922430 run: 2922430
For evsel(software/cpu-clock/) val: 2914966 enable: 2916549 run: 2916549
For evsel(software/cpu-clock/) val: 2910027 enable: 2911589 run: 2911589
#

Signed-off-by: Gautam Menghani <[e-mail]>
Tested-by: Arnaldo Carvalho de Melo <[e-mail]>
Cc: Adrian Hunter <[e-mail]>
Cc: Alexander Shishkin <[e-mail]>
Cc: Howard Chu <[e-mail]>
Cc: Ingo Molnar <[e-mail]>
Cc: Jiri Olsa <[e-mail]>
Cc: Kan Liang <[e-mail]>
Cc: Madhavan Srinivasan <[e-mail]>
Cc: Mark Rutland <[e-mail]>
Cc: Namhyung Kim <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
[ make the API take a CPU and thread then compute from these the appropriate indices. ]
Signed-off-by: Ian Rogers <[e-mail]>
Link: https://lore.kernel.org/linux-perf-users/CAP-5=fWb-=[e-mail]/
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/perf/python/counting.py

···
+#!/usr/bin/env python3
+# SPDX-License-Identifier: GPL-2.0
+# -*- python -*-
+# -*- coding: utf-8 -*-
+
+import argparse
+import perf
+
+def main(event: str):
+    evlist = perf.parse_events(event)
+
+    for evsel in evlist:
+        evsel.read_format = perf.FORMAT_TOTAL_TIME_ENABLED | perf.FORMAT_TOTAL_TIME_RUNNING
+
+    evlist.open()
+    evlist.enable()
+
+    count = 100000
+    while count > 0:
+        count -= 1
+
+    evlist.disable()
+
+    for evsel in evlist:
+        for cpu in evsel.cpus():
+            for thread in evsel.threads():
+                counts = evsel.read(cpu, thread)
+                print(f"For {evsel} val: {counts.val} enable: {counts.ena} run: {counts.run}")
+
+    evlist.close()
+
+if __name__ == '__main__':
+    ap = argparse.ArgumentParser()
+    ap.add_argument('-e', '--event', help="Events to open", default="cpu-clock,task-clock")
+    args = ap.parse_args()
+    main(args.event)