perf tools: Force uncore events to system wide monitoring

Make system wide (-a) the default option if no target was specified and
one of following conditions is met:

  - there's no workload specified (current behaviour)
  - there is workload specified but all requested
    events are system wide ones

Mixed events core/uncore with workload:

  $ perf stat -e 'uncore_cbox_0/clockticks/,cycles' sleep 1

   Performance counter stats for 'sleep 1':

     <not supported>      uncore_cbox_0/clockticks/
             980,489      cycles

         1.000897406 seconds time elapsed

Uncore event with workload:

  $ perf stat -e 'uncore_cbox_0/clockticks/' sleep 1

   Performance counter stats for 'system wide':

  281,473,897,192,670      uncore_cbox_0/clockticks/

         1.000833784 seconds time elapsed

Committer note:

When testing I realized the default case for !root, i.e. no events
passed via -e, was broke by v2 of this patch, reported and after a
patch provided by Jiri it is back working:

  [acme@jouet linux]$ perf stat usleep 1

   Performance counter stats for 'usleep 1':

         0.401335      task-clock:u (msec)     #   0.297 CPUs utilized
                0      context-switches:u      #   0.000 K/sec
                0      cpu-migrations:u        #   0.000 K/sec
               48      page-faults:u           #   0.120 M/sec
          458,146      cycles:u                #   1.142 GHz
          245,113      instructions:u          #   0.54  insn per cycle
           47,991      branches:u              # 119.578 M/sec
            4,022      branch-misses:u         #   8.38% of all branches

      0.001350029 seconds time elapsed

  [acme@jouet linux]$

Suggested-and-Tested-by: Borislav Petkov <bp@alien8.de>
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/20170227094818.GA12764@krava
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/builtin-stat.c

@@ -2350,6 +2350,35 @@ static int __cmd_report(int argc, const char **argv)
 	return 0;
 }
 
+static void setup_system_wide(int forks)
+{
+	/*
+	 * Make system wide (-a) the default target if
+	 * no target was specified and one of following
+	 * conditions is met:
+	 *
+	 *   - there's no workload specified
+	 *   - there is workload specified but all requested
+	 *     events are system wide events
+	 */
+	if (!target__none(&target))
+		return;
+
+	if (!forks)
+		target.system_wide = true;
+	else {
+		struct perf_evsel *counter;
+
+		evlist__for_each_entry(evsel_list, counter) {
+			if (!counter->system_wide)
+				return;
+		}
+
+		if (evsel_list->nr_entries)
+			target.system_wide = true;
+	}
+}
+
 int cmd_stat(int argc, const char **argv, const char *prefix __maybe_unused)
 {
 	const char * const stat_usage[] = {
@@ -2456,9 +2485,7 @@ 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;
 
-	/* Make system wide (-a) the default target. */
+	setup_system_wide(argc);
-	if (!argc && target__none(&target))
-		target.system_wide = true;
 
 	if (run_count < 0) {
 		pr_err("Run count must be a positive number\n");

tools/perf/util/parse-events.c

@@ -318,6 +318,7 @@ __add_event(struct list_head *list, int *idx,
 	(*idx)++;
 	evsel->cpus        = cpu_map__get(cpus);
 	evsel->own_cpus    = cpu_map__get(cpus);
+	evsel->system_wide = !!cpus;
 
 	if (name)
 		evsel->name = strdup(name);