perf diff: Add -q/--quiet option

The -q/--quiet option is to suppress any message. Sometimes users just
want to see the numbers and it can be used for that case.

Committer notes:

Before:

# perf diff | head -10
Failed to open /tmp/perf-6678.map, continuing without symbols
Failed to open /tmp/perf-6678.map, continuing without symbols
Failed to open /tmp/perf-2646.map, continuing without symbols
# Event 'cycles'
#
# Baseline Delta Abs Shared Object Symbol
# ........ ......... .......................... ............................................
#
5.36% -1.76% [kernel.vmlinux] [k] intel_idle
2.80% +1.48% firefox [.] 0x00000000000101fe
57.12% -1.25% libxul.so [.] 0x00000000009bea92
1.36% -1.11% [kernel.vmlinux] [k] __schedule
4.26% -1.00% perf-6678.map [.] 0x00007fac4b0e9320

After:

# perf diff -q | head -10
5.36% -1.76% [kernel.vmlinux] [k] intel_idle
2.80% +1.48% firefox [.] 0x00000000000101fe
57.12% -1.25% libxul.so [.] 0x00000000009bea92
1.36% -1.11% [kernel.vmlinux] [k] __schedule
4.26% -1.00% perf-6678.map [.] 0x00007fac4b0e9320
1.86% +0.95% [kernel.vmlinux] [k] update_blocked_averages
0.80% -0.70% [kernel.vmlinux] [k] native_sched_clock
0.74% -0.58% [kernel.vmlinux] [k] native_write_msr
0.76% -0.56% qemu-system-x86_64 [.] 0x00000000002395c0
+0.54% libpulsecommon-10.0.so [.] 0x000000000002d91b
#

Signed-off-by: Namhyung Kim <[e-mail]>
Suggested-and-Tested-by: Arnaldo Carvalho de Melo <[e-mail]>
Cc: Jiri Olsa <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: [e-mail]
Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/perf/Documentation/perf-diff.txt

···
 	Be verbose, for instance, show the raw counts in addition to the
 	diff.
 
+-q::
+--quiet::
+	Do not show any message.  (Suppress -v)
+
 -f::
 --force::
         Don't do ownership validation.

tools/perf/builtin-diff.c

···
 	hists__precompute(hists);
 	hists__output_resort(hists, NULL);
 
-	hists__fprintf(hists, true, 0, 0, 0, stdout,
+	hists__fprintf(hists, !quiet, 0, 0, 0, stdout,
 		       symbol_conf.use_callchain);
 }
 
···
 				hists__link(hists_base, hists);
 		}
 
-		fprintf(stdout, "%s# Event '%s'\n#\n", first ? "" : "\n",
-			perf_evsel__name(evsel_base));
+		if (!quiet) {
+			fprintf(stdout, "%s# Event '%s'\n#\n", first ? "" : "\n",
+				perf_evsel__name(evsel_base));
+		}
 
 		first = false;
 
-		if (verbose > 0 || data__files_cnt > 2)
+		if (verbose > 0 || ((data__files_cnt > 2) && !quiet))
 			data__fprintf();
 
 		/* Don't sort callchain for perf diff */
···
 static const struct option options[] = {
 	OPT_INCR('v', "verbose", &verbose,
 		    "be more verbose (show symbol address, etc)"),
+	OPT_BOOLEAN('q', "quiet", &quiet, "Do not show any message"),
 	OPT_BOOLEAN('b', "baseline-only", &show_baseline_only,
 		    "Show only items with match in baseline"),
 	OPT_CALLBACK('c', "compute", &compute,
···
 	perf_config(diff__config, NULL);
 
 	argc = parse_options(argc, argv, options, diff_usage, 0);
+
+	if (quiet)
+		perf_quiet_option();
 
 	if (symbol__init(NULL) < 0)
 		return -1;