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

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Message-ID: <CAHp75VdTndAD1gyLE_e8m9AaxrRMCNpYEu22+tWe1xrAz8oKBw@mail.gmail.com>
Date:   Thu, 1 Apr 2021 12:50:31 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Yury Norov <yury.norov@...il.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-m68k <linux-m68k@...ts.linux-m68k.org>,
        Linux-Arch <linux-arch@...r.kernel.org>,
        Linux-SH <linux-sh@...r.kernel.org>,
        Alexey Klimov <aklimov@...hat.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        David Sterba <dsterba@...e.com>,
        Dennis Zhou <dennis@...nel.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Jianpeng Ma <jianpeng.ma@...el.com>,
        Joe Perches <joe@...ches.com>,
        John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Rich Felker <dalias@...c.org>,
        Stefano Brivio <sbrivio@...hat.com>,
        Wei Yang <richard.weiyang@...ux.alibaba.com>,
        Wolfram Sang <wsa+renesas@...g-engineering.com>,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>
Subject: Re: [PATCH v6 00/12] lib/find_bit: fast path for small bitmaps

On Thu, Apr 1, 2021 at 12:29 PM Arnd Bergmann <arnd@...db.de> wrote:
>
> On Thu, Apr 1, 2021 at 11:16 AM Andy Shevchenko
> <andy.shevchenko@...il.com> wrote:
> >
> > On Thu, Apr 1, 2021 at 3:36 AM Yury Norov <yury.norov@...il.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