linux-kernel - Re: [PATCH] all: remove GENERIC_FIND_FIRST

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Message-ID: <20210526183322.GB20055@willie-the-truck>
Date:   Wed, 26 May 2021 19:33:23 +0100
From:   Will Deacon <will@...nel.org>
To:     Yury Norov <yury.norov@...il.com>
Cc:     linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
        Alexander Lobakin <alobakin@...me>,
        Alexey Klimov <aklimov@...hat.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Anton Ivanov <anton.ivanov@...bridgegreys.com>,
        Arnd Bergmann <arnd@...db.de>, Borislav Petkov <bp@...en8.de>,
        Catalin Marinas <catalin.marinas@....com>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Dan Williams <dan.j.williams@...el.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Ingo Molnar <mingo@...hat.com>,
        Jacob Keller <jacob.e.keller@...el.com>,
        Jarkko Sakkinen <jarkko@...nel.org>,
        Jeff Dike <jdike@...toit.com>,
        Kees Cook <keescook@...omium.org>,
        Mark Brown <broonie@...nel.org>,
        Matti Vaittinen <matti.vaittinen@...rohmeurope.com>,
        Nick Terrell <terrelln@...com>,
        Palmer Dabbelt <palmerdabbelt@...gle.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Richard Weinberger <richard@....at>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Vijayanand Jitta <vjitta@...eaurora.org>,
        Vineet Gupta <vgupta@...opsys.com>,
        Yogesh Lal <ylal@...eaurora.org>
Subject: Re: [PATCH] all: remove GENERIC_FIND_FIRST_BIT

On Mon, May 10, 2021 at 04:34:21PM -0700, Yury Norov wrote:
> In the 5.12 cycle we enabled the GENERIC_FIND_FIRST_BIT config option
> for ARM64 and MIPS. It increased performance and shrunk .text size; and
> so far I didn't receive any negative feedback on the change.
> 
> https://lore.kernel.org/linux-arch/20210225135700.1381396-1-yury.norov@gmail.com/
> 
> I think it's time to make all architectures use find_{first,last}_bit()
> unconditionally and remove the corresponding config option.
> 
> This patch doesn't introduce functional changes for arc, arm64, mips,
> s390 and x86 because they already enable GENERIC_FIND_FIRST_BIT. There
> will be no changes for arm because it implements find_{first,last}_bit
> in arch code. For other architectures I expect improvement both in
> performance and .text size.
> 
> It would be great if people with an access to real hardware would share
> the output of bloat-o-meter and lib/find_bit_benchmark.
> 
> Signed-off-by: Yury Norov <yury.norov@...il.com>
> ---
>  arch/arc/Kconfig                  |  1 -
>  arch/arm64/Kconfig                |  1 -
>  arch/mips/Kconfig                 |  1 -
>  arch/s390/Kconfig                 |  1 -
>  arch/x86/Kconfig                  |  1 -
>  arch/x86/um/Kconfig               |  1 -
>  include/asm-generic/bitops/find.h | 12 ------------
>  lib/Kconfig                       |  3 ---
>  8 files changed, 21 deletions(-)

Acked-by: Will Deacon <will@...nel.org>

Will