[PATCH] perf stat: Start tool events when enable_on_exec is used

[TAKANO Mitsuhiro <takano32@gmail.com>]

duration_time is a tool PMU event emulated in perf, so the kernel never
sees it and enable_on_exec cannot start it.  perf stat enables the events
itself only when enable_on_exec is not used; with two or more events
target__enable_on_exec() is true, so the tool event is never started and
reads as zero:

  # perf stat -e duration_time -- sleep 0.1
          103813345      duration_time
  # perf stat -e task-clock,duration_time -- sleep 0.1
                    0      duration_time

The zero value also reaches the default CPUs_utilized metric, which
divides by duration_time, so a plain `perf stat` prints "nan CPUs".

Start the tool events explicitly when enable_on_exec is used.  The second
command above then reports 103991394 and the default output prints
"0.0 CPUs" rather than "nan CPUs".

Verified on an arm64 box (Ampere Altra, Neoverse-N1), including the -r,
-I and group forms of the command; x86 was not tested.

Fixes: 0b18bced5444 ("perf tool_pmu: Make tool PMU events respect enable/disable")
Assisted-by: LLM
Signed-off-by: TAKANO Mitsuhiro <takano32@gmail.com>
---
 tools/perf/builtin-stat.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/tools/perf/builtin-stat.c b/tools/perf/builtin-stat.c
index c50cf230f16e..2062623682fb 100644
--- a/tools/perf/builtin-stat.c
+++ b/tools/perf/builtin-stat.c
@@ -510,6 +510,15 @@ static int enable_counters(void)
 	if (!target__enable_on_exec(&target)) {
 		if (!all_counters_use_bpf)
 			evlist__enable(evsel_list);
+	} else {
+		/*
+		 * Tool events are emulated in perf, so enable_on_exec above
+		 * does not start them.
+		 */
+		evlist__for_each_entry(evsel_list, evsel) {
+			if (evsel__is_tool(evsel))
+				evsel__enable(evsel);
+		}
 	}
 	return 0;
 }

base-commit: f47d223627f80cb7a1eb14c585fe6cb35de5e984
-- 
2.53.0