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From:   Alexey Klimov <aklimov@redhat.com>
Date:   Mon, 14 Jun 2021 16:45:29 +0100
Message-ID: <CAFBcO+9+kiqo-5RXqVuFGdA4yAV0o=zeJaenLZ5zryP-CQfAQQ@mail.gmail.com>
Subject: Re: [PATCH 5/8] lib: add find_first_and_bit()
To:     Yury Norov <yury.norov@gmail.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Cc:     linux-arch@vger.kernel.org,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>,
        Yoshinori Sato <ysato@users.sourceforge.jp>,
        Brian Cain <bcain@codeaurora.org>,
        Geert Uytterhoeven <geert@linux-m68k.org>,
        Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
        Jonas Bonn <jonas@southpole.se>,
        Stefan Kristiansson <stefan.kristiansson@saunalahti.fi>,
        "James E.J. Bottomley" <James.Bottomley@hansenpartnership.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Heiko Carstens <hca@linux.ibm.com>,
        Rich Felker <dalias@libc.org>,
        David Hildenbrand <david@redhat.com>,
        Jaegeuk Kim <jaegeuk@kernel.org>,
        Arnd Bergmann <arnd@arndb.de>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Rasmus Villemoes <linux@rasmusvillemoes.dk>,
        Andrew Morton <akpm@linux-foundation.org>,
        Alexander Lobakin <alobakin@pm.me>,
        Samuel Mendoza-Jonas <sam@mendozajonas.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Daniel Bristot de Oliveira <bristot@redhat.com>,
        Ingo Molnar <mingo@redhat.com>
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On Sat, Jun 12, 2021 at 1:36 PM Yury Norov <yury.norov@gmail.com> wrote:
>
> Currently find_first_and_bit() is an alias to find_next_and_bit(). However,
> it is widely used in cpumask, so it worth to optimize it. This patch adds
> its own implementation for find_first_and_bit().
>
> On x86_64 find_bit_benchmark says:
>
> Before (#define find_first_and_bit(...) find_next_and_bit(..., 0):
> Start testing find_bit() with random-filled bitmap
> [  140.291468] find_first_and_bit:           46890919 ns,  32671 iterations
> Start testing find_bit() with sparse bitmap
> [  140.295028] find_first_and_bit:               7103 ns,      1 iterations
>
> After:
> Start testing find_bit() with random-filled bitmap
> [  162.574907] find_first_and_bit:           25045813 ns,  32846 iterations
> Start testing find_bit() with sparse bitmap
> [  162.578458] find_first_and_bit:               4900 ns,      1 iterations
>
> (Thanks to Alexey Klimov for thorough testing.)
>
> Signed-off-by: Yury Norov <yury.norov@gmail.com>

Tested-by: Alexey Klimov <aklimov@redhat.com>

[..]

Best regards,
Alexey