[PATCH v5 1/2] lib/test_bitops: Add benchmark test for fns()

[Kuan-Wei Chiu]

Introduce a benchmark test for the fns(). It measures the total time
taken by fns() to process 10,000 test data generated using
get_random_bytes() for each n in the range [0, BITS_PER_LONG).

example:
test_bitops: fns:             7637268 ns

Signed-off-by: Kuan-Wei Chiu <visitorckw@xxxxxxxxx>
Suggested-by: Yury Norov <yury.norov@xxxxxxxxx>
---

Changes in v5:
- Reduce testing iterations from 1000000 to 10000 to decrease testing
  time.
- Move 'buf' inside the function.
- Mark 'buf' as __initdata.
- Assign the results of fns() to a volatile variable to prevent
  compiler optimization.
- Remove the iteration count from the benchmark result.

 lib/test_bitops.c | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/lib/test_bitops.c b/lib/test_bitops.c
index 3b7bcbee84db..5c627b525a48 100644
--- a/lib/test_bitops.c
+++ b/lib/test_bitops.c
@@ -50,6 +50,26 @@ static unsigned long order_comb_long[][2] = {
 };
 #endif
 
+static int __init test_fns(void)
+{
+	static unsigned long buf[10000] __initdata;
+	static volatile __used unsigned long tmp __initdata;
+	unsigned int i, n;
+	ktime_t time;
+
+	get_random_bytes(buf, sizeof(buf));
+	time = ktime_get();
+
+	for (n = 0; n < BITS_PER_LONG; n++)
+		for (i = 0; i < 10000; i++)
+			tmp = fns(buf[i], n);
+
+	time = ktime_get() - time;
+	pr_err("fns:  %18llu ns\n", time);
+
+	return 0;
+}
+
 static int __init test_bitops_startup(void)
 {
 	int i, bit_set;
@@ -94,6 +114,8 @@ static int __init test_bitops_startup(void)
 	if (bit_set != BITOPS_LAST)
 		pr_err("ERROR: FOUND SET BIT %d\n", bit_set);
 
+	test_fns();
+
 	pr_info("Completed bitops test\n");
 
 	return 0;
-- 
2.34.1