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 <namhyung@kernel.org>
Suggested-and-Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: kernel-team@lge.com
Link: http://lkml.kernel.org/r/20170217081742.17417-5-namhyung@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/Documentation/perf-diff.txt

@@ -73,6 +73,10 @@ OPTIONS
 	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

@@ -691,7 +691,7 @@ static void hists__process(struct hists *hists)
 	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);
 }
 
@@ -739,12 +739,14 @@ static void data_process(void)
 				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 */
@@ -807,6 +809,7 @@ static const char * const diff_usage[] = {
 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,
@@ -1328,6 +1331,9 @@ int cmd_diff(int argc, const char **argv, const char *prefix __maybe_unused)
 
 	argc = parse_options(argc, argv, options, diff_usage, 0);
 
+	if (quiet)
+		perf_quiet_option();
+
 	if (symbol__init(NULL) < 0)
 		return -1;