Hi Jaegeuk, Changman
Just a simple test, not very sure it can address
our qualm.
Bitmap size:216(the same as f2fs dentry_bits).
CPU: Intel i5 x86_64.
Time counting based on tsc(the less the fast).
[Index of 1] find_next_bit_le test_bit_le
0 20 117
1 20 114
2 20 113
3 20 139
4 22 121
5 22 118
6 22 115
8 22 112
9 22 106
10 22 105
11 22 100
16 22 98
48 22 97
80 27 95
104 27 92
136 32 95
160 32 92
184 32 90
200 27 87
208 35 84
According to the result, find_next_bit_le is always
better than test_bit_le, though there may be some
noise, but I think the result is clear.
Hope it can help us.:)
ps.The sample is attached too.
Thanks,
Gu
On 07/02/2014 06:30 PM, Jaegeuk Kim wrote:
> Thanks Changman for reminding this. :)
>
> If there are a lot of ones in the bit stream, find_next_bit_le would cause some
> overhead to translate the bits.
>
> However, it would be effective to use find_next_bit_le if the bit stream looks
> like 0000000001.
>
> Well, IMO the former case would be a little bit more common.
>
> Gu,
> Can you provide some performance numbers wrt this?
>
> On Tue, Jun 24, 2014 at 06:20:41PM +0800, Gu Zheng wrote:
>> Use find_next_bit_le rather than test_bit_le to improve search speed
>> lightly.
>>
>> Signed-off-by: Gu Zheng <guz.fnst@xxxxxxxxxxxxxx>
>> ---
>> fs/f2fs/dir.c | 43 +++++++++++++++++++++----------------------
>> 1 files changed, 21 insertions(+), 22 deletions(-)
>>
>> diff --git a/fs/f2fs/dir.c b/fs/f2fs/dir.c
>> index 3edd561..ba510fb 100644
>> --- a/fs/f2fs/dir.c
>> +++ b/fs/f2fs/dir.c
>> @@ -93,42 +93,41 @@ static struct f2fs_dir_entry *find_in_block(struct page *dentry_page,
>> const char *name, size_t namelen, int *max_slots,
>> f2fs_hash_t namehash, struct page **res_page)
>> {
>> - struct f2fs_dir_entry *de;
>> - unsigned long bit_pos = 0;
>> + unsigned long bit_pos = 0, bit_start = 0;
>> struct f2fs_dentry_block *dentry_blk = kmap(dentry_page);
>> const void *dentry_bits = &dentry_blk->dentry_bitmap;
>> - int max_len = 0;
>>
>> - while (bit_pos < NR_DENTRY_IN_BLOCK) {
>> - if (!test_bit_le(bit_pos, dentry_bits)) {
>> - if (bit_pos == 0)
>> - max_len = 1;
>> - else if (!test_bit_le(bit_pos - 1, dentry_bits))
>> - max_len++;
>> - bit_pos++;
>> - continue;
>> + while (bit_start < NR_DENTRY_IN_BLOCK) {
>> + struct f2fs_dir_entry *de;
>> + int max_len = 0;
>> +
>> + bit_pos = find_next_bit_le(dentry_bits,
>> + NR_DENTRY_IN_BLOCK, bit_start);
>> +
>> + max_len = bit_pos - bit_start;
>> + if (max_len > *max_slots) {
>> + *max_slots = max_len;
>> + max_len = 0;
>> }
>> +
>> + if (bit_pos >= NR_DENTRY_IN_BLOCK)
>> + break;
>> +
>> de = &dentry_blk->dentry[bit_pos];
>> if (early_match_name(name, namelen, namehash, de)) {
>> if (!memcmp(dentry_blk->filename[bit_pos],
>> name, namelen)) {
>> *res_page = dentry_page;
>> - goto found;
>> + return de;
>> }
>> }
>> - if (max_len > *max_slots) {
>> - *max_slots = max_len;
>> - max_len = 0;
>> - }
>> - bit_pos += GET_DENTRY_SLOTS(le16_to_cpu(de->name_len));
>> +
>> + bit_start = bit_pos
>> + + GET_DENTRY_SLOTS(le16_to_cpu(de->name_len));
>> }
>>
>> - de = NULL;
>> kunmap(dentry_page);
>> -found:
>> - if (max_len > *max_slots)
>> - *max_slots = max_len;
>> - return de;
>> + return NULL;
>> }
>>
>> static struct f2fs_dir_entry *find_in_level(struct inode *dir,
>> --
>> 1.7.7
>
#include <linux/module.h>
__u8 bitmaps[20][27] = {
{1, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0},
{2, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0},
{4, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0},
{8, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0},
{16, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 1,
0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0},
{32, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0},
{64, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0},
{0, 1, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0},
{0, 2, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0},
{0, 4, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0},
{0, 8, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0},
{0, 0, 1, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0},
{0, 0, 0, 0, 0, 0, 1,
0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0},
{0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 1, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0},
{0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 1,
0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0},
{0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 1, 0, 0, 0,
0, 0, 0, 0, 0, 0},
{0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 1,
0, 0, 0, 0, 0, 0},
{0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0,
0, 0, 1, 0, 0, 0},
{0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 1, 0},
{0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 1}
};
uint64_t rdtsc(void) {
uint32_t lo, hi;
__asm__ __volatile__ ("rdtsc" : "=a" (lo), "=d" (hi));
return (uint64_t)hi << 32 | lo;
}
static void test_bit_search_speed(void)
{
unsigned long flags;
uint64_t tsc_s, tsc_diff;
int i, j, pos;
const void *bit_addr;
local_irq_save(flags);
preempt_disable();
for (i = 0; i < 20; i++) {
printk("Test bitmap %d... \n", i);
bit_addr = &bitmaps[i];
tsc_s = rdtsc();
for (j = 0; j < 1000; j++)
find_next_bit_le(bit_addr, 216, 0);
tsc_diff = (rdtsc() - tsc_s)/1000;
printk("find_next_bit_le: %llu \n", tsc_diff);
pos = 0;
tsc_s = rdtsc();
for (j = 0; j < 1000; j++)
while (!test_bit_le(pos++, bit_addr));
tsc_diff = (rdtsc() - tsc_s)/1000;
printk("test_bit_le : %llu \n", tsc_diff);
}
preempt_enable();
local_irq_restore(flags);
}
static int __init start_test(void) {
test_bit_search_speed();
return 0;
}
static void __exit exit_test(void) {
}
module_init(start_test);
module_exit(exit_test);
MODULE_LICENSE("GPL");
MODULE_AUTHOR("Gu Zheng");
