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f2fs: optimize __find_rev_next_bit 

1. Skip __reverse_ulong if the bitmap is empty.
2. Reduce branches and codes.
According to my test, the performance of this new version is 5% higher on
an empty bitmap of 64bytes, and remains about the same in the worst scenario.

Signed-off-by: Fan li <fanofcode.li@samsung.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
This commit is contained in:
Fan Li 2015-11-12 08:43:04 +08:00 committed by Jaegeuk Kim
parent eb7e813cc7
commit 692223d132
1 changed files with 18 additions and 28 deletions
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46
fs/f2fs/segment.c
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@ -86,6 +86,7 @@ static inline unsigned long __reverse_ffs(unsigned long word)
/*
* __find_rev_next(_zero)_bit is copied from lib/find_next_bit.c because
* f2fs_set_bit makes MSB and LSB reversed in a byte.
* @size must be integral times of unsigned long.
* Example:
* MSB <--> LSB
* f2fs_set_bit(0, bitmap) => 1000 0000
@ -95,47 +96,36 @@ static unsigned long __find_rev_next_bit(const unsigned long *addr,
unsigned long size, unsigned long offset)
{
const unsigned long *p = addr + BIT_WORD(offset);
unsigned long result = offset & ~(BITS_PER_LONG - 1);
unsigned long result = size;
unsigned long tmp;
if (offset >= size)
return size;
size -= result;
size -= (offset & ~(BITS_PER_LONG - 1));
offset %= BITS_PER_LONG;
if (!offset)
goto aligned;
tmp = __reverse_ulong((unsigned char *)p);
tmp &= ~0UL >> offset;
while (1) {
if (*p == 0)
goto pass;
if (size < BITS_PER_LONG)
goto found_first;
if (tmp)
goto found_middle;
size -= BITS_PER_LONG;
result += BITS_PER_LONG;
p++;
aligned:
while (size & ~(BITS_PER_LONG-1)) {
tmp = __reverse_ulong((unsigned char *)p);
tmp &= ~0UL >> offset;
if (size < BITS_PER_LONG)
tmp &= (~0UL << (BITS_PER_LONG - size));
if (tmp)
goto found_middle;
result += BITS_PER_LONG;
goto found;
pass:
if (size <= BITS_PER_LONG)
break;
size -= BITS_PER_LONG;
offset = 0;
p++;
}
if (!size)
return result;
tmp = __reverse_ulong((unsigned char *)p);
found_first:
tmp &= (~0UL << (BITS_PER_LONG - size));
if (!tmp) /* Are any bits set? */
return result + size; /* Nope. */
found_middle:
return result + __reverse_ffs(tmp);
return result;
found:
return result - size + __reverse_ffs(tmp);
}
static unsigned long __find_rev_next_zero_bit(const unsigned long *addr,