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Date:   Tue, 11 May 2021 13:53:22 +0000
To:     Yury Norov <yury.norov@gmail.com>
From:   Alexander Lobakin <alobakin@pm.me>
Cc:     Alexander Lobakin <alobakin@pm.me>, linux-kernel@vger.kernel.org,
        linux-arch@vger.kernel.org, Alexey Klimov <aklimov@redhat.com>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
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        Catalin Marinas <catalin.marinas@arm.com>,
        Christian Borntraeger <borntraeger@de.ibm.com>,
        Dan Williams <dan.j.williams@intel.com>,
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        Jacob Keller <jacob.e.keller@intel.com>,
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        Will Deacon <will@kernel.org>, Yogesh Lal <ylal@codeaurora.org>
Reply-To: Alexander Lobakin <alobakin@pm.me>
Subject: Re: [PATCH] all: remove GENERIC_FIND_FIRST_BIT
Message-ID: <20210511134551.18721-1-alobakin@pm.me>
In-Reply-To: <20210510233421.18684-1-yury.norov@gmail.com>
References: <20210510233421.18684-1-yury.norov@gmail.com>
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From: Yury Norov <yury.norov@gmail.com>
Date: Mon, 10 May 2021 16:34:21 -0700

> 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@gm=
ail.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@gmail.com>
> ---
>  arch/arc/Kconfig                  |  1 -
>  arch/arm64/Kconfig                |  1 -
>  arch/mips/Kconfig                 |  1 -

MIPS bit:

Reviewed-by: Alexander Lobakin <alobakin@pm.me>
Tested-by: Alexander Lobakin <alobakin@pm.me>

>  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(-)

Thanks,
Al