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

From: Ian Rogers
Date: Mon Nov 22 2021 - 21:03:51 EST

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
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
Invalid event (uncore_imc/cas_count_read/) in per-thread mode, enable system wide with '-a'.

Signed-off-by: Ian Rogers <irogers@xxxxxxxxxx>
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));
return scnprintf(msg, size, "Cannot collect data source with the load latency event alone. "