linux-kernel - [PATCH v2 5/7] perf stat: When no events, don't report an error if there is none

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Message-ID: <20251203214706.112174-6-irogers@google.com>
Date: Wed,  3 Dec 2025 13:47:04 -0800
From: Ian Rogers <irogers@...gle.com>
To: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>, 
	Arnaldo Carvalho de Melo <acme@...nel.org>, Namhyung Kim <namhyung@...nel.org>, 
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>, Jiri Olsa <jolsa@...nel.org>, 
	Ian Rogers <irogers@...gle.com>, Adrian Hunter <adrian.hunter@...el.com>, 
	James Clark <james.clark@...aro.org>, Thomas Richter <tmricht@...ux.ibm.com>, 
	linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH v2 5/7] perf stat: When no events, don't report an error if
 there is none

Events may fail to open as no supported CPUs were specified on the
command line. In this case a confusing "error" message of "success"
can be reported. Let's skip the error in that case.

Before:
```
$ perf stat -C2048 -e cycles -- true
WARNING: A requested CPU in '2048' is not supported by PMU 'cpu' (CPUs 0-7) for event 'cycles'
Error:
No supported events found.
The sys_perf_event_open() syscall returned with 0 (Success) for event (cpu/unknown-hardware/).
"dmesg | grep -i perf" may provide additional information.
```

After:
```
$ perf stat -C2048 -e cycles -- true
WARNING: A requested CPU in '2048' is not supported by PMU 'cpu' (CPUs 0-7) for event 'cycles'
Error:
No supported events found.
```

Signed-off-by: Ian Rogers <irogers@...gle.com>
---
 tools/perf/builtin-stat.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/tools/perf/builtin-stat.c b/tools/perf/builtin-stat.c
index 6410115ed9c5..bd3c3de8d200 100644
--- a/tools/perf/builtin-stat.c
+++ b/tools/perf/builtin-stat.c
@@ -924,8 +924,10 @@ static int __run_perf_stat(int argc, const char **argv, int run_idx)
 		}
 	}
 	if (!has_supported_counters && !stat_config.null_run) {
-		evsel__open_strerror(evlist__first(evsel_list), &target, open_err,
-				     msg, sizeof(msg));
+		if (open_err) {
+			evsel__open_strerror(evlist__first(evsel_list), &target, open_err,
+					     msg, sizeof(msg));
+		}
 		ui__error("No supported events found.\n%s\n", msg);

 		if (child_pid != -1)
-- 
2.52.0.177.g9f829587af-goog