[RFC] Improve workload error in 'perf record'

[RFC] Improve workload error in 'perf record'

[Arnaldo Carvalho de Melo]

Hi,

	Please take a look,

Best regards,

- Arnaldo

Arnaldo Carvalho de Melo (2):
  perf evlist: Add a method to return the list of evsels as a string
  perf record: Improve 'Workload failed' message printing events + what
    was exec'ed

 tools/perf/builtin-record.c |  8 ++++++--
 tools/perf/util/evlist.c    | 19 +++++++++++++++++++
 tools/perf/util/evlist.h    |  2 ++
 3 files changed, 27 insertions(+), 2 deletions(-)

-- 
2.26.2

[PATCH 1/2] perf evlist: Add a method to return the list of evsels as a string

[Arnaldo Carvalho de Melo]

From: Arnaldo Carvalho de Melo <acme@redhat.com>

Add a 'scnprintf' method to obtain the list of evsels in a evlist as a
string, excluding the "dummy" event used for things like receiving
metadata events (PERF_RECORD_FORK, MMAP, etc) when synthesizing
preexisting threads.

Will be used to improve the error message for workload failure in 'perf
record.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
---
 tools/perf/util/evlist.c | 19 +++++++++++++++++++
 tools/perf/util/evlist.h |  2 ++
 2 files changed, 21 insertions(+)

diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c
index f1c79ecf81073f74..d29a8a118973c71c 100644
--- a/tools/perf/util/evlist.c
+++ b/tools/perf/util/evlist.c
@@ -2138,3 +2138,22 @@ struct evsel *evlist__find_evsel(struct evlist *evlist, int idx)
 	}
 	return NULL;
 }
+
+int evlist__scnprintf_evsels(struct evlist *evlist, size_t size, char *bf)
+{
+	struct evsel *evsel;
+	int printed = 0;
+
+	evlist__for_each_entry(evlist, evsel) {
+		if (evsel__is_dummy_event(evsel))
+			continue;
+		if (size > (strlen(evsel__name(evsel)) + (printed ? 2 : 1))) {
+			printed += scnprintf(bf + printed, size - printed, "%s%s", printed ? "," : "", evsel__name(evsel));
+		} else {
+			printed += scnprintf(bf + printed, size - printed, "%s...", printed ? "," : "");
+			break;
+		}
+	}
+
+	return printed;
+}
diff --git a/tools/perf/util/evlist.h b/tools/perf/util/evlist.h
index b695ffaae519a5d0..a8b97b50cceb7e43 100644
--- a/tools/perf/util/evlist.h
+++ b/tools/perf/util/evlist.h
@@ -365,4 +365,6 @@ int evlist__ctlfd_ack(struct evlist *evlist);
 #define EVLIST_DISABLED_MSG "Events disabled\n"
 
 struct evsel *evlist__find_evsel(struct evlist *evlist, int idx);
+
+int evlist__scnprintf_evsels(struct evlist *evlist, size_t size, char *bf);
 #endif /* __PERF_EVLIST_H */
-- 
2.26.2

[PATCH 2/2] perf record: Improve 'Workload failed' message printing events + what was exec'ed

[Arnaldo Carvalho de Melo]

From: Arnaldo Carvalho de Melo <acme@redhat.com>

Before:

  # perf record -a cycles,instructions,cache-misses
  Workload failed: No such file or directory
  #

After:

  # perf record -a cycles,instructions,cache-misses
  Failed to collect 'cycles' for the 'cycles,instructions,cache-misses' workload: No such file or directory
  #

Helps disambiguating other error scenarios:

  # perf record -a -e cycles,instructions,cache-misses bla
  Failed to collect 'cycles,instructions,cache-misses' for the 'bla' workload: No such file or directory
  # perf record -a cycles,instructions,cache-misses sleep 1
  Failed to collect 'cycles' for the 'cycles,instructions,cache-misses' workload: No such file or directory
  #

When all goes well we're back to the usual:

  # perf record -a -e cycles,instructions,cache-misses sleep 1
  [ perf record: Woken up 3 times to write data ]
  [ perf record: Captured and wrote 3.151 MB perf.data (21242 samples) ]
  #

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
---
 tools/perf/builtin-record.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
index 35465d1db6dda3ae..5fb9665a2ec27dde 100644
--- a/tools/perf/builtin-record.c
+++ b/tools/perf/builtin-record.c
@@ -1977,9 +1977,13 @@ static int __cmd_record(struct record *rec, int argc, const char **argv)
 		record__auxtrace_snapshot_exit(rec);
 
 	if (forks && workload_exec_errno) {
-		char msg[STRERR_BUFSIZE];
+		char msg[STRERR_BUFSIZE], strevsels[2048];
 		const char *emsg = str_error_r(workload_exec_errno, msg, sizeof(msg));
-		pr_err("Workload failed: %s\n", emsg);
+
+		evlist__scnprintf_evsels(rec->evlist, sizeof(strevsels), strevsels);
+
+		pr_err("Failed to collect '%s' for the '%s' workload: %s\n",
+			strevsels, argv[0], emsg);
 		err = -1;
 		goto out_child;
 	}
-- 
2.26.2

Re: [RFC] Improve workload error in 'perf record'

[Ian Rogers]

On Wed, Apr 14, 2021 at 6:16 AM Arnaldo Carvalho de Melo
<acme@kernel.org> wrote:
>
> Hi,
>
>         Please take a look,
>
> Best regards,

Acked-by: Ian Rogers <irogers@google.com>

Having been confused by this for a case in the past, thanks! It'd be
nice for code coverage's sake to have a shell test on this.

Thanks,
Ian

> - Arnaldo
>
> Arnaldo Carvalho de Melo (2):
>   perf evlist: Add a method to return the list of evsels as a string
>   perf record: Improve 'Workload failed' message printing events + what
>     was exec'ed
>
>  tools/perf/builtin-record.c |  8 ++++++--
>  tools/perf/util/evlist.c    | 19 +++++++++++++++++++
>  tools/perf/util/evlist.h    |  2 ++
>  3 files changed, 27 insertions(+), 2 deletions(-)
>
> --
> 2.26.2
>