Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit 27fae429 authored by Jens Axboe's avatar Jens Axboe
Browse files

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: default avatarOmar Sandoval <osandov@fb.com>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent b2c5d16b

lib/sbitmap.c

+13 −8
Original line number Diff line number Diff line
@@ -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) {

			index = 0;

		alloc_hint = 0;

		}

		if (++index >= sb->map_nr)

			index = 0;

	}



	return nr;