linux-kernel - [PATCH 2/2] perf evsel: Improve error message for uncore events

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Message-Id: <20211123020341.3073673-2-irogers@google.com>
Date:   Mon, 22 Nov 2021 18:03:41 -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>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Andi Kleen <ak@...ux.intel.com>,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     eranian@...gle.com, Ian Rogers <irogers@...gle.com>
Subject: [PATCH 2/2] perf evsel: Improve error message for uncore events

When a group has multiple events and the leader fails it can yield
errors like:

$ perf stat -e '{uncore_imc/cas_count_read/},instructions' /bin/true
Error:
The sys_perf_event_open() syscall returned with 22 (Invalid argument) for event (uncore_imc/cas_count_read/).
/bin/dmesg | grep -i perf may provide additional information.

However, when not the group leader <not supported> is given:

$ perf stat -e '{instructions,uncore_imc/cas_count_read/}' /bin/true
...
         1,619,057      instructions
   <not supported> MiB  uncore_imc/cas_count_read/

This is necessary because get_group_fd will fail if the leader fails and
is the direct result of the check on line 750 of builtin-stat.c in
stat_handle_error that returns COUNTER_SKIP for the latter case.

This patch improves the error message to:

$ perf stat -e '{uncore_imc/cas_count_read/},instructions' /bin/true
Error:
Invalid event (uncore_imc/cas_count_read/) in per-thread mode, enable system wide with '-a'.

Signed-off-by: Ian Rogers <irogers@...gle.com>
---
 tools/perf/util/evsel.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
index a59fb2ecb84e..48696ff4bddb 100644
--- a/tools/perf/util/evsel.c
+++ b/tools/perf/util/evsel.c
@@ -2950,6 +2950,11 @@ int evsel__open_strerror(struct evsel *evsel, struct target *target,
 			return scnprintf(msg, size, "wrong clockid (%d).", clockid);
 		if (perf_missing_features.aux_output)
 			return scnprintf(msg, size, "The 'aux_output' feature is not supported, update the kernel.");
+		if ((evsel__leader(evsel) == evsel) &&
+		    (evsel->core.leader->nr_members > 1))
+			return scnprintf(msg, size,
+	"Invalid event (%s) in per-thread mode, enable system wide with '-a'.",
+					evsel__name(evsel));
 		break;
 	case ENODATA:
 		return scnprintf(msg, size, "Cannot collect data source with the load latency event alone. "
-- 
2.34.0.rc2.393.gf8c9666880-goog