perf report: Add report.group config option

Add report.group config option for setting default value of event
group view.  It affects the report output only if perf.data contains
event group info.

A user can write .perfconfig file like below to enable group view by
default:

  $ cat ~/.perfconfig
  [report]
  group = true

And it can be disabled through command line:

  $ perf report --no-group
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/r/1358845787-1350-19-git-send-email-namhyung@kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/builtin-report.c

@@ -8,6 +8,7 @@
 #include "builtin.h"
 
 #include "util/util.h"
+#include "util/cache.h"
 
 #include "util/annotate.h"
 #include "util/color.h"
@@ -54,6 +55,16 @@ struct perf_report {
 	DECLARE_BITMAP(cpu_bitmap, MAX_NR_CPUS);
 };
 
+static int perf_report_config(const char *var, const char *value, void *cb)
+{
+	if (!strcmp(var, "report.group")) {
+		symbol_conf.event_group = perf_config_bool(var, value);
+		return 0;
+	}
+
+	return perf_default_config(var, value, cb);
+}
+
 static int perf_report__add_branch_hist_entry(struct perf_tool *tool,
 					struct addr_location *al,
 					struct perf_sample *sample,
@@ -677,6 +688,8 @@ int cmd_report(int argc, const char **argv, const char *prefix __maybe_unused)
 	OPT_END()
 	};
 
+	perf_config(perf_report_config, NULL);
+
 	argc = parse_options(argc, argv, options, report_usage, 0);
 
 	if (report.use_stdio)