linux-kernel - Re: [PATCH 5/8] lib: add find_first_and

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Date:   Mon, 14 Jun 2021 16:45:29 +0100
From:   Alexey Klimov <aklimov@...hat.com>
To:     Yury Norov <yury.norov@...il.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Cc:     linux-arch@...r.kernel.org,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        Brian Cain <bcain@...eaurora.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Jonas Bonn <jonas@...thpole.se>,
        Stefan Kristiansson <stefan.kristiansson@...nalahti.fi>,
        "James E.J. Bottomley" <James.Bottomley@...senpartnership.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Rich Felker <dalias@...c.org>,
        David Hildenbrand <david@...hat.com>,
        Jaegeuk Kim <jaegeuk@...nel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Alexander Lobakin <alobakin@...me>,
        Samuel Mendoza-Jonas <sam@...dozajonas.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH 5/8] lib: add find_first_and_bit()

On Sat, Jun 12, 2021 at 1:36 PM Yury Norov <yury.norov@...il.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@...il.com>

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

[..]

Best regards,
Alexey