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

From: Andy Shevchenko <andy.shevchenko@gmail.com>
To: Arnd Bergmann <arnd@arndb.de>
Cc: Yury Norov <yury.norov@gmail.com>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	linux-m68k <linux-m68k@lists.linux-m68k.org>,
	Linux-Arch <linux-arch@vger.kernel.org>,
	Linux-SH <linux-sh@vger.kernel.org>,
	Alexey Klimov <aklimov@redhat.com>,
	Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
	David Sterba <dsterba@suse.com>, Dennis Zhou <dennis@kernel.org>,
	Geert Uytterhoeven <geert@linux-m68k.org>,
	Jianpeng Ma <jianpeng.ma@intel.com>,
	Joe Perches <joe@perches.com>,
	John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>,
	Josh Poimboeuf <jpoimboe@redhat.com>,
	Rasmus Villemoes <linux@rasmusvillemoes.dk>,
	Rich Felker <dalias@libc.org>,
	Stefano Brivio <sbrivio@redhat.com>,
	Wei Yang <richard.weiyang@linux.alibaba.com>,
	Wolfram Sang <wsa+renesas@sang-engineering.com>,
	Yoshinori Sato <ysato@users.sourceforge.jp>
Subject: Re: [PATCH v6 00/12] lib/find_bit: fast path for small bitmaps
Date: Thu, 1 Apr 2021 12:50:31 +0300	[thread overview]
Message-ID: <CAHp75VdTndAD1gyLE_e8m9AaxrRMCNpYEu22+tWe1xrAz8oKBw@mail.gmail.com> (raw)
In-Reply-To: <CAK8P3a2EGc4BS7UTyC6=ySgLEoyqbswh1Gh_=M21NmhRThssYQ@mail.gmail.com>

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