2020-12-12 04:20:40

by Yun Levi

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 <[email protected]>
---
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