[PATCH] lib/find_bit_benchmark: avoid clearing randomly filled bitmap in test_find_first_bit()

[Akinobu Mita]

test_find_first_bit() searches for a set bit from the beginning of the
test bitmap and clears it repeatedly, eventually clearing the entire
bitmap.

After test_find_first_bit() is executed, test_find_first_and_bit() and
test_find_next_and_bit() are executed without randomly reinitializing the
cleared bitmap.

In the first phase (testing find_bit() with a random-filled bitmap),
test_find_first_bit() only operates on 1/10 of the entire size of the
testing bitmap, so this isn't a big problem.

However, in the second phase (testing find_bit() with a sparse bitmap),
test_find_first_bit() clears the entire test bitmap, so the subsequent
test_find_first_and_bit() and test_find_next_and_bit() will not find any
set bits. This is probably not the intended benchmark.

To fix this issue, test_find_first_bit() operates on a duplicated bitmap
and does not clear the original test bitmap.
The same is already done in test_find_first_and_bit().

While we're at it, add const qualifiers to the bitmap pointer arguments
in the test functions.

Signed-off-by: Akinobu Mita <akinobu.mita@xxxxxxxxx>
Cc: Yury Norov <yury.norov@xxxxxxxxx>
Cc: Rasmus Villemoes <linux@xxxxxxxxxxxxxxxxxx>
---
 lib/find_bit_benchmark.c | 15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/lib/find_bit_benchmark.c b/lib/find_bit_benchmark.c
index 402e160e7186..00d9dc61cd46 100644
--- a/lib/find_bit_benchmark.c
+++ b/lib/find_bit_benchmark.c
@@ -30,18 +30,20 @@ static DECLARE_BITMAP(bitmap, BITMAP_LEN) __initdata;
 static DECLARE_BITMAP(bitmap2, BITMAP_LEN) __initdata;
 
 /*
- * This is Schlemiel the Painter's algorithm. It should be called after
- * all other tests for the same bitmap because it sets all bits of bitmap to 1.
+ * This is Schlemiel the Painter's algorithm.
  */
-static int __init test_find_first_bit(void *bitmap, unsigned long len)
+static int __init test_find_first_bit(const void *bitmap, unsigned long len)
 {
+	static DECLARE_BITMAP(cp, BITMAP_LEN) __initdata;
 	unsigned long i, cnt;
 	ktime_t time;
 
+	bitmap_copy(cp, bitmap, BITMAP_LEN);
+
 	time = ktime_get();
 	for (cnt = i = 0; i < len; cnt++) {
-		i = find_first_bit(bitmap, len);
-		__clear_bit(i, bitmap);
+		i = find_first_bit(cp, len);
+		__clear_bit(i, cp);
 	}
 	time = ktime_get() - time;
 	pr_err("find_first_bit:     %18llu ns, %6ld iterations\n", time, cnt);
@@ -49,7 +51,8 @@ static int __init test_find_first_bit(void *bitmap, unsigned long len)
 	return 0;
 }
 
-static int __init test_find_first_and_bit(void *bitmap, const void *bitmap2, unsigned long len)
+static int __init test_find_first_and_bit(const void *bitmap, const void *bitmap2,
+		unsigned long len)
 {
 	static DECLARE_BITMAP(cp, BITMAP_LEN) __initdata;
 	unsigned long i, cnt;
-- 
2.43.0