sbitmap: don't loop for find_next_zero_bit() for !round_robin (27fae429) · Commits · 戴 / test

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>

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;

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