[PATCH 4/5] perf stat: Add -a as a default target

[Jiri Olsa]

Boris asked for default -a option in case we monitor
only uncore events. While implementing that I thought
it might be actually useful to make it overall default.

  # perf stat
  Warning: No target specified, setting system-wide collection (-a).
  ...

Requested-by: Borislav Petkov <bp@xxxxxxxxx>
Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: David Ahern <dsahern@xxxxxxxxx>
Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
Cc: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Link: http://lkml.kernel.org/n/tip-tq11of2qlz8kxpxzva05d54l@xxxxxxxxxxxxxx
---
 tools/perf/Documentation/perf-stat.txt | 2 +-
 tools/perf/builtin-stat.c              | 6 ++++--
 2 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/tools/perf/Documentation/perf-stat.txt b/tools/perf/Documentation/perf-stat.txt
index d96ccd4844df..aecf2a87e7d6 100644
--- a/tools/perf/Documentation/perf-stat.txt
+++ b/tools/perf/Documentation/perf-stat.txt
@@ -63,7 +63,7 @@ report::
 
 -a::
 --all-cpus::
-        system-wide collection from all CPUs
+        system-wide collection from all CPUs (default if no target is specified)
 
 -c::
 --scale::
diff --git a/tools/perf/builtin-stat.c b/tools/perf/builtin-stat.c
index f28719178b51..0d09ec7029d3 100644
--- a/tools/perf/builtin-stat.c
+++ b/tools/perf/builtin-stat.c
@@ -2445,8 +2445,10 @@ int cmd_stat(int argc, const char **argv, const char *prefix __maybe_unused)
 	} else if (big_num_opt == 0) /* User passed --no-big-num */
 		big_num = false;
 
-	if (!argc && target__none(&target))
-		usage_with_options(stat_usage, stat_options);
+	if (!argc && target__none(&target)) {
+		pr_warning("Warning: No target specified, setting system-wide collection (-a).\n");
+		target.system_wide = true;
+	}
 
 	if (run_count < 0) {
 		pr_err("Run count must be a positive number\n");
-- 
2.7.4