On Thu, Nov 29, 2018 at 12:47:49PM -0700, Jens Axboe wrote: > 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 <osan...@fb.com> > Signed-off-by: Jens Axboe <ax...@kernel.dk> > > --- > > Since v1: > > - Reset alloc_hint if we loop for the round-robin case > - Update commit message > > diff --git a/lib/sbitmap.c b/lib/sbitmap.c > index fdd1b8aa8ac6..45cab6bbc1c7 100644 > --- a/lib/sbitmap.c > +++ b/lib/sbitmap.c > @@ -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; > -- > Jens Axboe >