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sbitmap: don't loop for find_next_zero_bit() for !round_robin 

If we aren't forced to do round robin tag allocation, just use the
allocation hint to find the index for the tag word, don't use it for the
offset inside the word. This avoids a potential extra round trip in the
bit looping, and since we're fetching this cacheline, we may as well
check the whole word from the start.

Reviewed-by: Omar Sandoval <osandov@fb.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Jens Axboe 2018-11-29 12:35:16 -07:00
parent b2c5d16b72
commit 27fae429ac
1 changed files with 13 additions and 8 deletions
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21
lib/sbitmap.c
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@ -118,10 +118,19 @@ int sbitmap_get(struct sbitmap *sb, unsigned int alloc_hint, bool round_robin)
index = SB_NR_TO_INDEX(sb, alloc_hint);
/*
* Unless we're doing round robin tag allocation, just use the
* alloc_hint to find the right word index. No point in looping
* twice in find_next_zero_bit() for that case.
*/
if (round_robin)
alloc_hint = SB_NR_TO_BIT(sb, alloc_hint);
else
alloc_hint = 0;
for (i = 0; i < sb->map_nr; i++) {
nr = __sbitmap_get_word(&sb->map[index].word,
sb->map[index].depth,
SB_NR_TO_BIT(sb, alloc_hint),
sb->map[index].depth, alloc_hint,
!round_robin);
if (nr != -1) {
nr += index << sb->shift;
@ -129,13 +138,9 @@ int sbitmap_get(struct sbitmap *sb, unsigned int alloc_hint, bool round_robin)
}
/* Jump to next index. */
index++;
alloc_hint = index << sb->shift;
if (index >= sb->map_nr) {
alloc_hint = 0;
if (++index >= sb->map_nr)
index = 0;
alloc_hint = 0;
}
}
return nr;