perf stat: Display user and system time

Adding the support to read rusage data once the workload is finished and
display the system/user time values:

  $ perf stat --null perf bench sched pipe
  ...

   Performance counter stats for 'perf bench sched pipe':

       5.342599256 seconds time elapsed

       2.544434000 seconds user
       4.549691000 seconds sys

It works only in non -r mode and only for workload target.

So as of now, for workload targets, we display 3 types of timings. The
time we meassure in perf stat from enable to disable+period:

       5.342599256 seconds time elapsed

The time spent in user and system lands, displayed only for workload
session/target:

       2.544434000 seconds user
       4.549691000 seconds sys

Those times are the very same displayed by 'time' tool.  They are
returned by wait4 call via the getrusage struct interface.

Committer notes:

Had to rename some variables to avoid this on older systems such as
centos:6:

  builtin-stat.c: In function 'print_footer':
  builtin-stat.c:1831: warning: declaration of 'stime' shadows a global declaration
  /usr/include/time.h:297: warning: shadowed declaration is here

Committer testing:

  # perf stat --null time perf bench sched pipe
  # Running 'sched/pipe' benchmark:
  # Executed 1000000 pipe operations between two processes

       Total time: 5.526 [sec]

         5.526534 usecs/op
           180945 ops/sec
  1.00user 6.25system 0:05.52elapsed 131%CPU (0avgtext+0avgdata 8056maxresident)k
  0inputs+0outputs (0major+606minor)pagefaults 0swaps

   Performance counter stats for 'time perf bench sched pipe':

         5.530978744 seconds time elapsed

         1.004037000 seconds user
         6.259937000 seconds sys

  #
Suggested-by: NIngo Molnar <mingo@kernel.org>
Signed-off-by: NJiri Olsa <jolsa@kernel.org>
Tested-by: NArnaldo Carvalho de Melo <acme@redhat.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20180605121313.31337-1-jolsa@kernel.orgSigned-off-by: NArnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/Documentation/perf-stat.txt

@@ -310,20 +310,38 @@ Users who wants to get the actual value can apply --no-metric-only.
 EXAMPLES
 --------
 
-$ perf stat -- make -j
+$ perf stat -- make
 
- Performance counter stats for 'make -j':
+   Performance counter stats for 'make':
 
-    8117.370256  task clock ticks     #      11.281 CPU utilization factor
-            678  context switches     #       0.000 M/sec
-            133  CPU migrations       #       0.000 M/sec
-         235724  pagefaults           #       0.029 M/sec
-    24821162526  CPU cycles           #    3057.784 M/sec
-    18687303457  instructions         #    2302.138 M/sec
-      172158895  cache references     #      21.209 M/sec
-       27075259  cache misses         #       3.335 M/sec
+        83723.452481      task-clock:u (msec)       #    1.004 CPUs utilized
+                   0      context-switches:u        #    0.000 K/sec
+                   0      cpu-migrations:u          #    0.000 K/sec
+           3,228,188      page-faults:u             #    0.039 M/sec
+     229,570,665,834      cycles:u                  #    2.742 GHz
+     313,163,853,778      instructions:u            #    1.36  insn per cycle
+      69,704,684,856      branches:u                #  832.559 M/sec
+       2,078,861,393      branch-misses:u           #    2.98% of all branches
 
- Wall-clock time elapsed:   719.554352 msecs
+        83.409183620 seconds time elapsed
+
+        74.684747000 seconds user
+         8.739217000 seconds sys
+
+TIMINGS
+-------
+As displayed in the example above we can display 3 types of timings.
+We always display the time the counters were enabled/alive:
+
+        83.409183620 seconds time elapsed
+
+For workload sessions we also display time the workloads spent in
+user/system lands:
+
+        74.684747000 seconds user
+         8.739217000 seconds sys
+
+Those times are the very same as displayed by the 'time' tool.
 
 CSV FORMAT
 ----------

tools/perf/builtin-stat.c

@@ -80,6 +80,9 @@
 #include <sys/stat.h>
 #include <sys/wait.h>
 #include <unistd.h>
+#include <sys/time.h>
+#include <sys/resource.h>
+#include <sys/wait.h>
 
 #include "sane_ctype.h"
 
@@ -175,6 +178,8 @@ static int			output_fd;
 static int			print_free_counters_hint;
 static int			print_mixed_hw_group_error;
 static u64			*walltime_run;
+static bool			ru_display			= false;
+static struct rusage		ru_data;
 
 struct perf_stat {
 	bool			 record;
@@ -726,7 +731,7 @@ static int __run_perf_stat(int argc, const char **argv, int run_idx)
 					break;
 			}
 		}
-		waitpid(child_pid, &status, 0);
+		wait4(child_pid, &status, 0, &ru_data);
 
 		if (workload_exec_errno) {
 			const char *emsg = str_error_r(workload_exec_errno, msg, sizeof(msg));
@@ -1804,6 +1809,11 @@ static void print_table(FILE *output, int precision, double avg)
 	fprintf(output, "\n%*s# Final result:\n", indent, "");
 }
 
+static double timeval2double(struct timeval *t)
+{
+	return t->tv_sec + (double) t->tv_usec/USEC_PER_SEC;
+}
+
 static void print_footer(void)
 {
 	double avg = avg_stats(&walltime_nsecs_stats) / NSEC_PER_SEC;
@@ -1815,6 +1825,15 @@ static void print_footer(void)
 
 	if (run_count == 1) {
 		fprintf(output, " %17.9f seconds time elapsed", avg);
+
+		if (ru_display) {
+			double ru_utime = timeval2double(&ru_data.ru_utime);
+			double ru_stime = timeval2double(&ru_data.ru_stime);
+
+			fprintf(output, "\n\n");
+			fprintf(output, " %17.9f seconds user\n", ru_utime);
+			fprintf(output, " %17.9f seconds sys\n", ru_stime);
+		}
 	} else {
 		double sd = stddev_stats(&walltime_nsecs_stats) / NSEC_PER_SEC;
 		/*
@@ -2950,6 +2969,13 @@ int cmd_stat(int argc, const char **argv)
 
 	setup_system_wide(argc);
 
+	/*
+	 * Display user/system times only for single
+	 * run and when there's specified tracee.
+	 */
+	if ((run_count == 1) && target__none(&target))
+		ru_display = true;
+
 	if (run_count < 0) {
 		pr_err("Run count must be a positive number\n");
 		parse_options_usage(stat_usage, stat_options, "r", 1);