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

From: Jiri Olsa
Date: Sun Nov 28 2021 - 12:00:23 EST


On Mon, Nov 22, 2021 at 06:03:41PM -0800, Ian Rogers wrote:
> 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@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));

should we rather check 'target' pointer for the per-thread mode?
I'm not sure that per-thread mode will always be the case for the failure

jirka

> break;
> case ENODATA:
> return scnprintf(msg, size, "Cannot collect data source with the load latency event alone. "
> --
> 2.34.0.rc2.393.gf8c9666880-goog
>