[PATCH] improve lib/test_find_bit

[Yury Norov]

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;
* rename test_find_bit.c to find_bit_benchmark.c.

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

Signed-off-by: Yury Norov <ynorov@xxxxxxxxxxxxxxxxxx>
---
 lib/Kconfig.debug                             |  2 +-
 lib/Makefile                                  |  2 +-
 lib/{test_find_bit.c => find_bit_benchmark.c} | 47 ++++++++++++---------------
 3 files changed, 23 insertions(+), 28 deletions(-)
 rename lib/{test_find_bit.c => find_bit_benchmark.c} (79%)

diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 138034cc68a3..1c57c36ad79a 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -1838,7 +1838,7 @@ config TEST_BPF
 
 	  If unsure, say N.
 
-config TEST_FIND_BIT
+config FIND_BIT_BENCHMARK
 	tristate "Test find_bit functions"
 	default n
 	help
diff --git a/lib/Makefile b/lib/Makefile
index 97ec69d843f2..1688cc84536e 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -45,8 +45,8 @@ obj-$(CONFIG_TEST_STRING_HELPERS) += test-string_helpers.o
 obj-y += hexdump.o
 obj-$(CONFIG_TEST_HEXDUMP) += test_hexdump.o
 obj-y += kstrtox.o
+obj-$(CONFIG_FIND_BIT_BENCHMARK) += find_bit_benchmark.o
 obj-$(CONFIG_TEST_BPF) += test_bpf.o
-obj-$(CONFIG_TEST_FIND_BIT) += test_find_bit.o
 obj-$(CONFIG_TEST_FIRMWARE) += test_firmware.o
 obj-$(CONFIG_TEST_SYSCTL) += test_sysctl.o
 obj-$(CONFIG_TEST_HASH) += test_hash.o test_siphash.o
diff --git a/lib/test_find_bit.c b/lib/find_bit_benchmark.c
similarity index 79%
rename from lib/test_find_bit.c
rename to lib/find_bit_benchmark.c
index f4394a36f9aa..67b19233c28f 100644
--- a/lib/test_find_bit.c
+++ b/lib/find_bit_benchmark.c
@@ -43,16 +43,15 @@ static DECLARE_BITMAP(bitmap, BITMAP_LEN) __initdata;
 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;
 }
@@ -60,14 +59,13 @@ static int __init test_find_first_bit(void *bitmap, unsigned long len)
 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;
 }
@@ -75,14 +73,13 @@ static int __init test_find_next_bit(const void *bitmap, unsigned long len)
 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;
 }
@@ -90,9 +87,9 @@ static int __init test_find_next_zero_bit(const void *bitmap, unsigned long len)
 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);
@@ -100,9 +97,8 @@ static int __init test_find_last_bit(const void *bitmap, unsigned long 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;
 }
@@ -132,13 +128,12 @@ static int __init find_bit_test(void)
 	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");
-- 
2.11.0