[PATCH] perf stat: Do not show stats if workload fails

[David Ahern <dsahern@gmail.com>]

Currently perf-stat attempts to show counter stats even if the workload
is bogus:

$ perf stat -- foo
foo: No such file or directory

 Performance counter stats for 'foo':

     <not counted>      task-clock
     <not counted>      context-switches
     <not counted>      cpu-migrations
     <not counted>      page-faults
     <not counted>      cycles
     <not counted>      stalled-cycles-frontend
     <not counted>      stalled-cycles-backend
     <not counted>      instructions
     <not counted>      branches
     <not counted>      branch-misses

       0.009769943 seconds time elapsed

It is impossible to differentiate all the failure modes, but it seems
reasonable that if the workload handling fails, perf-stat should not try
to print stats.

With this change:

$ perf stat  -v -- foo
Failed to start workload

Signed-off-by: David Ahern <dsahern@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Stephane Eranian <eranian@google.com>
---
 tools/perf/builtin-stat.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/tools/perf/builtin-stat.c b/tools/perf/builtin-stat.c
index dab98b50c9fe..d6e6a0b031d9 100644
--- a/tools/perf/builtin-stat.c
+++ b/tools/perf/builtin-stat.c
@@ -586,7 +586,11 @@ static int __run_perf_stat(int argc, const char **argv)
 	clock_gettime(CLOCK_MONOTONIC, &ref_time);
 
 	if (forks) {
-		perf_evlist__start_workload(evsel_list);
+		if (perf_evlist__start_workload(evsel_list) != 0) {
+			pr_err("Failed to start workload\n");
+			return -1;
+		}
+
 		handle_initial_delay();
 
 		if (interval) {
@@ -1793,7 +1797,10 @@ int cmd_stat(int argc, const char **argv, const char *prefix __maybe_unused)
 				run_idx + 1);
 
 		status = run_perf_stat(argc, argv);
-		if (forever && status != -1) {
+		if (status < 0)
+			break;
+
+		if (forever) {
 			print_stat(argc, argv);
 			perf_stat__reset_stats(evsel_list);
 		}
-- 
1.8.3.4 (Apple Git-47)