tools/power turbostat: if --num_iterations, print for specific number of iterations

There's a use case during test to only print specific round of iterations
if --num_iterations is specified, for example, with this patch applied:

turbostat -i 5 -n 4
will capture 4 samples with 5 seconds interval.

[lenb: renamed to --num_iterations from --iterations]
Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Chen Yu <yu.c.chen@intel.com>
Reviewed-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>

tools/power/x86/turbostat/turbostat.8

@@ -67,6 +67,8 @@ The column name "all" can be used to enable all disabled-by-default built-in cou
 .PP
 \fB--interval seconds\fP overrides the default 5.0 second measurement interval.
 .PP
+\fB--num_iterations num\fP number of the measurement iterations.
+.PP
 \fB--out output_file\fP turbostat output is written to the specified output_file.
 The file is truncated if it already exists, and it is created if it does not exist.
 .PP

tools/power/x86/turbostat/turbostat.c

@@ -51,6 +51,7 @@ int *fd_percpu;
 struct timeval interval_tv = {5, 0};
 struct timespec interval_ts = {5, 0};
 struct timespec one_msec = {0, 1000000};
+unsigned int num_iterations;
 unsigned int debug;
 unsigned int quiet;
 unsigned int shown;
@@ -496,6 +497,7 @@ void help(void)
 	"--interval sec.subsec	Override default 5-second measurement interval\n"
 	"--help		print this help message\n"
 	"--list		list column headers only\n"
+	"--num_iterations num   number of the measurement iterations\n"
 	"--out file	create or truncate \"file\" for all output\n"
 	"--version	print version information\n"
 	"\n"
@@ -2763,6 +2765,7 @@ void turbostat_loop()
 {
 	int retval;
 	int restarted = 0;
+	int done_iters = 0;
 
 	setup_signal_handler();
 
@@ -2781,6 +2784,7 @@ void turbostat_loop()
 		goto restart;
 	}
 	restarted = 0;
+	done_iters = 0;
 	gettimeofday(&tv_even, (struct timezone *)NULL);
 
 	while (1) {
@@ -2809,6 +2813,8 @@ void turbostat_loop()
 		flush_output_stdout();
 		if (exit_requested)
 			break;
+		if (num_iterations && ++done_iters >= num_iterations)
+			break;
 		do_sleep();
 		if (snapshot_proc_sysfs_files())
 			goto restart;
@@ -2830,6 +2836,8 @@ void turbostat_loop()
 		flush_output_stdout();
 		if (exit_requested)
 			break;
+		if (num_iterations && ++done_iters >= num_iterations)
+			break;
 	}
 }
 
@@ -5212,6 +5220,7 @@ void cmdline(int argc, char **argv)
 		{"debug",	no_argument,		0, 'd'},	/* internal, not documented */
 		{"enable",	required_argument,	0, 'e'},
 		{"interval",	required_argument,	0, 'i'},
+		{"num_iterations",	required_argument,	0, 'n'},
 		{"help",	no_argument,		0, 'h'},
 		{"hide",	required_argument,	0, 'H'},	// meh, -h taken by --help
 		{"Joules",	no_argument,		0, 'J'},
@@ -5227,7 +5236,7 @@ void cmdline(int argc, char **argv)
 
 	progname = argv[0];
 
-	while ((opt = getopt_long_only(argc, argv, "+C:c:Dde:hi:Jo:qST:v",
+	while ((opt = getopt_long_only(argc, argv, "+C:c:Dde:hi:Jn:o:qST:v",
 				long_options, &option_index)) != -1) {
 		switch (opt) {
 		case 'a':
@@ -5287,6 +5296,15 @@ void cmdline(int argc, char **argv)
 		case 'q':
 			quiet = 1;
 			break;
+		case 'n':
+			num_iterations = strtod(optarg, NULL);
+
+			if (num_iterations <= 0) {
+				fprintf(outf, "iterations %d should be positive number\n",
+					num_iterations);
+				exit(2);
+			}
+			break;
 		case 's':
 			/*
 			 * --show: show only those specified