Re: [PATCH v6 00/12] lib/find_bit: fast path for small bitmaps

Andy Shevchenko
2021-04-01T09:51:38Z

On Thu, Apr 1, 2021 at 12:29 PM Arnd Bergmann <arnd@arndb.de> wrote:
>
> On Thu, Apr 1, 2021 at 11:16 AM Andy Shevchenko
> <andy.shevchenko@gmail.com> wrote:
> >
> > On Thu, Apr 1, 2021 at 3:36 AM Yury Norov <yury.norov@gmail.com> wrote:
> > >
> > > Bitmap operations are much simpler and faster in case of small bitmaps
> > > which fit into a single word. In linux/bitmap.c we have a machinery that
> > > allows compiler to replace actual function call with a few instructions
> > > if bitmaps passed into the function are small and their size is known at
> > > compile time.
> > >
> > > find_*_bit() API lacks this functionality; but users will benefit from it
> > > a lot. One important example is cpumask subsystem when
> > > NR_CPUS <= BITS_PER_LONG.
> >
> > Cool, thanks!
> >
> > I guess it's assumed to go via Andrew's tree.
> >
> > But after that since you are about to be a maintainer of this, I think
> > it would make sense to send PRs directly to Linus. I would recommend
> > creating an official tree (followed by an update in the MAINTAINERS)
> > and connecting it to Linux next (usually done by email to Stephen).
>
> It depends on how often we expect to see updates to this. I have not
> followed the changes as closely as I should have, but I can also
> merge them through the asm-generic tree for this time so Andrew
> has to carry fewer patches for this.
>
> I normally don't have a lot of material for asm-generic either, half
> the time there are no pull requests at all for a given release. I would
> expect future changes to the bitmap implementation to only need
> an occasional bugfix, which could go through either the asm-generic
> tree or through mm and doesn't need another separate pull request.
>
> If it turns out to be a tree that needs regular updates every time,
> then having a top level repository in linux-next would be appropriate.

Agree. asm-generic may serve for this. My worries are solely about how
much burden we add on Andrew's shoulders.

--
With Best Regards,
Andy Shevchenko