From: Yury Norov <yury.norov@gmail.com>
To: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: linux-m68k@lists.linux-m68k.org, linux-kernel@vger.kernel.org,
linux-sh@vger.kernel.org, linux-arch@vger.kernel.org,
Geert Uytterhoeven <geert@linux-m68k.org>,
Yoshinori Sato <ysato@users.sourceforge.jp>,
Rich Felker <dalias@libc.org>, Arnd Bergmann <arnd@arndb.de>,
Dennis Zhou <dennis@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
Wolfram Sang <wsa+renesas@sang-engineering.com>,
David Sterba <dsterba@suse.com>,
Stefano Brivio <sbrivio@redhat.com>,
"Ma, Jianpeng" <jianpeng.ma@intel.com>,
Wei Yang <richard.weiyang@linux.alibaba.com>,
Josh Poimboeuf <jpoimboe@redhat.com>,
John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>,
Joe Perches <joe@perches.com>
Subject: Re: [RESEND PATCH v2 0/6] lib/find_bit: fast path for small bitmaps
Date: Tue, 16 Feb 2021 10:00:42 -0800 [thread overview]
Message-ID: <20210216180042.GA421019@yury-ThinkPad> (raw)
In-Reply-To: <YCuM7yzMoXjpuj8Y@smile.fi.intel.com>
On Tue, Feb 16, 2021 at 11:14:23AM +0200, Andy Shevchenko wrote:
> On Mon, Feb 15, 2021 at 01:30:44PM -0800, Yury Norov wrote:
> > [add David Laight <David.Laight@ACULAB.COM> ]
> >
> > On Sat, Jan 30, 2021 at 11:17:11AM -0800, Yury Norov wrote:
> > > Bitmap operations are much simpler and faster in case of small bitmaps
> > > which fit into a single word. In linux/bitmap.h 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; despite users will benefit from
> > > it a lot. One important example is cpumask subsystem when
> > > NR_CPUS <= BITS_PER_LONG. In the very best case, the compiler may replace
> > > a find_*_bit() call for such a bitmap with a single ffs or ffz instruction.
> > >
> > > Tools is synchronized with new implementation where needed.
> > >
> > > v1: https://www.spinics.net/lists/kernel/msg3804727.html
> > > v2: - employ GENMASK() for bitmaps;
> > > - unify find_bit inliners in;
> > > - address comments to v1;
> >
> > Comments so far:
> > - increased image size (patch #8) - addressed by introducing
> > CONFIG_FAST_PATH;
>
> > - split tools and kernel parts - not clear why it's better.
>
> Because tools are user space programs and sometimes may not follow kernel
> specifics, so they are different logically and changes should be separated.
In this specific case tools follow kernel well.
Nevertheless, if you think it's a blocker for the series, I can split. What
option for tools is better for you - doubling the number of patches or
squashing everything in a patch bomb?
next prev parent reply other threads:[~2021-02-16 18:01 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-30 19:17 [RESEND PATCH v2 0/6] lib/find_bit: fast path for small bitmaps Yury Norov
2021-01-30 19:17 ` [PATCH 1/8] tools: disable -Wno-type-limits Yury Norov
2021-01-30 19:17 ` [PATCH 2/8] tools: bitmap: sync function declarations with linux kernel Yury Norov
2021-01-30 19:17 ` [PATCH 3/8] arch: rearrange headers inclusion order in asm/bitops for m68k and sh Yury Norov
2021-01-30 19:17 ` [PATCH 4/8] lib: introduce BITS_{FIRST,LAST} macro Yury Norov
2021-02-01 13:42 ` Andy Shevchenko
2021-01-30 19:17 ` [PATCH 5/8] bitsperlong.h: introduce SMALL_CONST() macro Yury Norov
2021-02-01 13:45 ` Andy Shevchenko
2021-02-02 7:10 ` Yury Norov
2021-01-30 19:17 ` [PATCH 6/8] lib: inline _find_next_bit() wrappers Yury Norov
2021-02-01 13:47 ` Andy Shevchenko
2021-02-02 7:13 ` Yury Norov
2021-01-30 19:17 ` [PATCH 7/8] lib: add fast path for find_next_*_bit() Yury Norov
2021-02-01 13:49 ` Andy Shevchenko
2021-02-01 16:02 ` David Laight
2021-02-01 16:22 ` 'Andy Shevchenko'
2021-02-02 7:02 ` Yury Norov
2021-01-30 19:17 ` [PATCH 8/8] lib: add fast path for find_first_*_bit() and find_last_bit() Yury Norov
2021-02-01 13:50 ` Andy Shevchenko
2021-02-15 21:30 ` [RESEND PATCH v2 0/6] lib/find_bit: fast path for small bitmaps Yury Norov
2021-02-16 9:14 ` Andy Shevchenko
2021-02-16 18:00 ` Yury Norov [this message]
2021-02-17 10:33 ` Andy Shevchenko
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