perf stat: Fix CSV mode column output for non-cgroup events

When using the -x option, perf stat prints CSV-style output with one
event per line.  For each event, it prints the count, the unit, the
event name, the cgroup, and a bunch of other event specific fields (such
as insn per cycles).

When you use CSV-style mode, you expect a normalized output where each
event is printed with the same number of fields regardless of what it is
so it can easily be imported into a spreadsheet or parsed.

For instance, if an event does not have a unit, then print an empty
field for it.

Although this approach was implemented for the unit, it was not for the
cgroup.

When mixing cgroup and non-cgroup events, then non-cgroup events would
not show an empty field, instead the next field was printed, make
columns not line up correctly.

This patch fixes the cgroup output issues by forcing an empty field
for non-cgroup events as soon as one event has cgroup.

Before:

  <not counted> @ @cycles @foo    @ 0    @100.00@@
  2531614       @ @cycles @6420922@100.00@    @

foo cgroup lines up with time_running!

After:

  <not counted> @ @cycles @foo @0       @100.00@@
  2594834       @ @cycles @    @5287372 @100.00@@

Fields line up.
Signed-off-by: Stephane Eranian <eranian@google.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1541587845-9150-1-git-send-email-eranian@google.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/stat-display.c

@@ -59,6 +59,15 @@ static void print_noise(struct perf_stat_config *config,
 	print_noise_pct(config, stddev_stats(&ps->res_stats[0]), avg);
 }
 
+static void print_cgroup(struct perf_stat_config *config, struct perf_evsel *evsel)
+{
+	if (nr_cgroups) {
+		const char *cgrp_name = evsel->cgrp ? evsel->cgrp->name  : "";
+		fprintf(config->output, "%s%s", config->csv_sep, cgrp_name);
+	}
+}
+
+
 static void aggr_printout(struct perf_stat_config *config,
 			  struct perf_evsel *evsel, int id, int nr)
 {
@@ -336,8 +345,7 @@ static void abs_printout(struct perf_stat_config *config,
 
 	fprintf(output, "%-*s", config->csv_output ? 0 : 25, perf_evsel__name(evsel));
 
-	if (evsel->cgrp)
-		fprintf(output, "%s%s", config->csv_sep, evsel->cgrp->name);
+	print_cgroup(config, evsel);
 }
 
 static bool is_mixed_hw_group(struct perf_evsel *counter)
@@ -431,9 +439,7 @@ static void printout(struct perf_stat_config *config, int id, int nr,
 			config->csv_output ? 0 : -25,
 			perf_evsel__name(counter));
 
-		if (counter->cgrp)
-			fprintf(config->output, "%s%s",
-				config->csv_sep, counter->cgrp->name);
+		print_cgroup(config, counter);
 
 		if (!config->csv_output)
 			pm(config, &os, NULL, NULL, "", 0);