Re: [PATCH 27/54] lib/bitmap: add bitmap_weight_{cmp, eq, gt, ge, lt, le} functions

[Yury Norov]

On Mon, Jan 24, 2022 at 4:42 AM Andy Shevchenko
<andriy.shevchenko@xxxxxxxxxxxxxxx> wrote:
>
> On Sun, Jan 23, 2022 at 10:38:58AM -0800, Yury Norov wrote:
> > Many kernel users use bitmap_weight() to compare the result against
> > some number or expression:
> >
> >       if (bitmap_weight(...) > 1)
> >               do_something();
> >
> > It works OK, but may be significantly improved for large bitmaps: if
> > first few words count set bits to a number greater than given, we can
> > stop counting and immediately return.
> >
> > The same idea would work in other direction: if we know that the number
> > of set bits that we counted so far is small enough, so that it would be
> > smaller than required number even if all bits of the rest of the bitmap
> > are set, we can stop counting earlier.
> >
> > This patch adds new bitmap_weight_cmp() as suggested by Michał Mirosław
> > and a family of eq, gt, ge, lt and le wrappers to allow this optimization.
>
> lt, and le
>
> > The following patches apply new functions where appropriate.
>
> What I missed in the above message is the rough statistics like some of them
> are used more often, some less, and some, perhaps, just added for the sake of
> symmetry (the latter is what would be important to see if there are APIs which
> have no users at all).

These are my grep numbers. Some lines are declarations and comments, so minus
6 or 8 for each number, but all new functions have actual users.

$ git grep weight_eq|wc -l
35
$ git grep weight_gt|wc -l
20
$ git grep weight_ge|wc -l
25
$ git grep weight_lt|wc -l
14
$ git grep weight_le|wc -l
18