lib/find_bit_benchmark.c: improvements

As suggested in review comments:
* printk: align numbers using whitespaces instead of tabs;
* return error value from init() to avoid calling rmmod if testing again;
* use ktime_get instead of get_cycles as some arches don't support it;

The output in dmesg (on QEMU arm64):
[ 38.823430] Start testing find_bit() with random-filled bitmap
[ 38.845358] find_next_bit: 20138448 ns, 163968 iterations
[ 38.856217] find_next_zero_bit: 10615328 ns, 163713 iterations
[ 38.863564] find_last_bit: 7111888 ns, 163967 iterations
[ 40.944796] find_first_bit: 2081007216 ns, 163968 iterations
[ 40.944975]
[ 40.944975] Start testing find_bit() with sparse bitmap
[ 40.945268] find_next_bit: 73216 ns, 656 iterations
[ 40.967858] find_next_zero_bit: 22461008 ns, 327025 iterations
[ 40.968047] find_last_bit: 62320 ns, 656 iterations
[ 40.978060] find_first_bit: 9889360 ns, 656 iterations

Link: http://lkml.kernel.org/r/20171124143040.a44jvhmnaiyedg2i@yury-thinkpad
Signed-off-by: Yury Norov <[e-mail]>
Tested-by: Geert Uytterhoeven <[e-mail]>
Cc: Alexey Dobriyan <[e-mail]>
Cc: Clement Courbet <[e-mail]>
Cc: Matthew Wilcox <[e-mail]>
Cc: Rasmus Villemoes <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

lib/find_bit_benchmark.c

···
 static int __init test_find_first_bit(void *bitmap, unsigned long len)
 {
 	unsigned long i, cnt;
-	cycles_t cycles;
+	ktime_t time;
 
-	cycles = get_cycles();
+	time = ktime_get();
 	for (cnt = i = 0; i < len; cnt++) {
 		i = find_first_bit(bitmap, len);
 		__clear_bit(i, bitmap);
 	}
-	cycles = get_cycles() - cycles;
-	pr_err("find_first_bit:\t\t%llu cycles,\t%ld iterations\n",
-	       (u64)cycles, cnt);
+	time = ktime_get() - time;
+	pr_err("find_first_bit:     %18llu ns, %6ld iterations\n", time, cnt);
 
 	return 0;
 }
···
 static int __init test_find_next_bit(const void *bitmap, unsigned long len)
 {
 	unsigned long i, cnt;
-	cycles_t cycles;
+	ktime_t time;
 
-	cycles = get_cycles();
+	time = ktime_get();
 	for (cnt = i = 0; i < BITMAP_LEN; cnt++)
 		i = find_next_bit(bitmap, BITMAP_LEN, i) + 1;
-	cycles = get_cycles() - cycles;
-	pr_err("find_next_bit:\t\t%llu cycles,\t%ld iterations\n",
-	       (u64)cycles, cnt);
+	time = ktime_get() - time;
+	pr_err("find_next_bit:      %18llu ns, %6ld iterations\n", time, cnt);
 
 	return 0;
 }
···
 static int __init test_find_next_zero_bit(const void *bitmap, unsigned long len)
 {
 	unsigned long i, cnt;
-	cycles_t cycles;
+	ktime_t time;
 
-	cycles = get_cycles();
+	time = ktime_get();
 	for (cnt = i = 0; i < BITMAP_LEN; cnt++)
 		i = find_next_zero_bit(bitmap, len, i) + 1;
-	cycles = get_cycles() - cycles;
-	pr_err("find_next_zero_bit:\t%llu cycles,\t%ld iterations\n",
-	       (u64)cycles, cnt);
+	time = ktime_get() - time;
+	pr_err("find_next_zero_bit: %18llu ns, %6ld iterations\n", time, cnt);
 
 	return 0;
 }
···
 static int __init test_find_last_bit(const void *bitmap, unsigned long len)
 {
 	unsigned long l, cnt = 0;
-	cycles_t cycles;
+	ktime_t time;
 
-	cycles = get_cycles();
+	time = ktime_get();
 	do {
 		cnt++;
 		l = find_last_bit(bitmap, len);
···
 			break;
 		len = l;
 	} while (len);
-	cycles = get_cycles() - cycles;
-	pr_err("find_last_bit:\t\t%llu cycles,\t%ld iterations\n",
-	       (u64)cycles, cnt);
+	time = ktime_get() - time;
+	pr_err("find_last_bit:      %18llu ns, %6ld iterations\n", time, cnt);
 
 	return 0;
 }
···
 	test_find_last_bit(bitmap, BITMAP_LEN);
 	test_find_first_bit(bitmap, BITMAP_LEN);
 
-	return 0;
+	/*
+	 * Everything is OK. Return error just to let user run benchmark
+	 * again without annoying rmmod.
+	 */
+	return -EINVAL;
 }
 module_init(find_bit_test);
-
-static void __exit test_find_bit_cleanup(void)
-{
-}
-module_exit(test_find_bit_cleanup);
 
 MODULE_LICENSE("GPL");