linux-kernel - [PATCH] lib/find_bit_bench: fix the unmatched iterations cnt

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Message-ID: <20201211085039.GA7619@ubuntu>
Date:   Fri, 11 Dec 2020 17:50:39 +0900
From:   Levi Yun <ppbuk5246@...il.com>
To:     dushistov@...l.ru, arnd@...db.de, akpm@...ux-foundation.org,
        gustavo@...eddedor.com, vilhelm.gray@...il.com,
        richard.weiyang@...ux.alibaba.com,
        andriy.shevchenko@...ux.intel.com, joseph.qi@...ux.alibaba.com,
        skalluru@...vell.com, yury.norov@...il.com, jpoimboe@...hat.com
Cc:     linux-kernel@...r.kernel.org
Subject: [PATCH] lib/find_bit_bench: fix the unmatched iterations cnt

We should have same iteration count when we walk the same bitmap
regardless of using find_next_bit or find_last_bit.

When we run the find_bit_benchmark.ko, we sometime get
unmatched iterations count below:

             Start testing find_bit() with random-filled bitmap
[+...] find_next_bit:                  875085 ns, 163755 iterations <
[+...] find_next_zero_bit:             865319 ns, 163926 iterations
[+...] find_last_bit:                  611807 ns, 163756 iterations <
[+...] find_first_bit:                1601016 ns,  16335 iterations
[+...] find_next_and_bit:              400645 ns,  74040 iterations
[+...]
              Start testing find_bit() with sparse bitmap
[+...] find_next_bit:                    9942 ns,    654 iterations
[+...] find_next_zero_bit:            1678445 ns, 327027 iterations
[+...] find_last_bit:                    7131 ns,    654 iterations
[+...] find_first_bit:                 551383 ns,    654 iterations
[+...] find_next_and_bit:                3027 ns,      1 iterations

Normally, this is happen when the last bit of bitmap was set.

This patch fix the unmatched iterations count between
test_find_next_bit and test_find_last_bit.

Signed-off-by: Levi Yun <ppbuk5246@...il.com>
---
 lib/find_bit_benchmark.c | 30 ++++++++++++++++--------------
 1 file changed, 16 insertions(+), 14 deletions(-)

diff --git a/lib/find_bit_benchmark.c b/lib/find_bit_benchmark.c
index 5637c5711db9..766e0487852b 100644
--- a/lib/find_bit_benchmark.c
+++ b/lib/find_bit_benchmark.c
@@ -35,14 +35,14 @@ static DECLARE_BITMAP(bitmap2, BITMAP_LEN) __initdata;
  */
 static int __init test_find_first_bit(void *bitmap, unsigned long len)
 {
-	unsigned long i, cnt;
+	unsigned long i = 0, cnt = 0;
 	ktime_t time;
 
 	time = ktime_get();
-	for (cnt = i = 0; i < len; cnt++) {
+	do {
 		i = find_first_bit(bitmap, len);
 		__clear_bit(i, bitmap);
-	}
+	} while (i++ < len && ++cnt);
 	time = ktime_get() - time;
 	pr_err("find_first_bit:     %18llu ns, %6ld iterations\n", time, cnt);
 
@@ -51,12 +51,13 @@ 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;
+	unsigned long i = 0, cnt = 0;
 	ktime_t time;
 
 	time = ktime_get();
-	for (cnt = i = 0; i < BITMAP_LEN; cnt++)
-		i = find_next_bit(bitmap, BITMAP_LEN, i) + 1;
+	do {
+		i = find_next_bit(bitmap, BITMAP_LEN, i);
+	} while (i++ < BITMAP_LEN && ++cnt);
 	time = ktime_get() - time;
 	pr_err("find_next_bit:      %18llu ns, %6ld iterations\n", time, cnt);
 
@@ -65,12 +66,13 @@ 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;
+	unsigned long i = 0, cnt = 0;
 	ktime_t time;
 
 	time = ktime_get();
-	for (cnt = i = 0; i < BITMAP_LEN; cnt++)
-		i = find_next_zero_bit(bitmap, len, i) + 1;
+	do {
+		i = find_next_zero_bit(bitmap, len, i);
+	} while (i++ < BITMAP_LEN && ++cnt);
 	time = ktime_get() - time;
 	pr_err("find_next_zero_bit: %18llu ns, %6ld iterations\n", time, cnt);
 
@@ -84,12 +86,11 @@ static int __init test_find_last_bit(const void *bitmap, unsigned long len)
 
 	time = ktime_get();
 	do {
-		cnt++;
 		l = find_last_bit(bitmap, len);
 		if (l >= len)
 			break;
 		len = l;
-	} while (len);
+	} while (len >= 0 && ++cnt);
 	time = ktime_get() - time;
 	pr_err("find_last_bit:      %18llu ns, %6ld iterations\n", time, cnt);
 
@@ -99,12 +100,13 @@ static int __init test_find_last_bit(const void *bitmap, unsigned long len)
 static int __init test_find_next_and_bit(const void *bitmap,
 		const void *bitmap2, unsigned long len)
 {
-	unsigned long i, cnt;
+	unsigned long i = 0, cnt = 0;
 	ktime_t time;
 
 	time = ktime_get();
-	for (cnt = i = 0; i < BITMAP_LEN; cnt++)
-		i = find_next_and_bit(bitmap, bitmap2, BITMAP_LEN, i + 1);
+	do {
+		i = find_next_and_bit(bitmap, bitmap2, BITMAP_LEN, i);
+	} while (i++ < BITMAP_LEN && ++cnt);
 	time = ktime_get() - time;
 	pr_err("find_next_and_bit:  %18llu ns, %6ld iterations\n", time, cnt);
 
-- 
2.27.0