linux-kernel - Re: [RESEND PATCH v2 0/6] lib/find_bit: fast path for small bitmaps

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <YCuM7yzMoXjpuj8Y@smile.fi.intel.com>
Date:   Tue, 16 Feb 2021 11:14:23 +0200
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Yury Norov <yury.norov@...il.com>
Cc:     linux-m68k@...ts.linux-m68k.org, linux-kernel@...r.kernel.org,
        linux-sh@...r.kernel.org, linux-arch@...r.kernel.org,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        Rich Felker <dalias@...c.org>, Arnd Bergmann <arnd@...db.de>,
        Dennis Zhou <dennis@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Wolfram Sang <wsa+renesas@...g-engineering.com>,
        David Sterba <dsterba@...e.com>,
        Stefano Brivio <sbrivio@...hat.com>,
        "Ma, Jianpeng" <jianpeng.ma@...el.com>,
        Wei Yang <richard.weiyang@...ux.alibaba.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>,
        Joe Perches <joe@...ches.com>
Subject: Re: [RESEND PATCH v2 0/6] lib/find_bit: fast path for small bitmaps

On Mon, Feb 15, 2021 at 01:30:44PM -0800, Yury Norov wrote:
> [add David Laight <David.Laight@...LAB.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.

>  Anything else?

-- 
With Best Regards,
Andy Shevchenko