Re: [PATCH] all: remove GENERIC_FIND_FIRST_BIT

From: Alexander Lobakin <alobakin@pm.me>
To: Yury Norov <yury.norov@gmail.com>
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>,
	Anton Ivanov <anton.ivanov@cambridgegreys.com>,
	Arnd Bergmann <arnd@arndb.de>, Borislav Petkov <bp@alien8.de>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Christian Borntraeger <borntraeger@de.ibm.com>,
	Dan Williams <dan.j.williams@intel.com>,
	"H. Peter Anvin" <hpa@zytor.com>,
	Heiko Carstens <hca@linux.ibm.com>,
	Ingo Molnar <mingo@redhat.com>,
	Jacob Keller <jacob.e.keller@intel.com>,
	Jarkko Sakkinen <jarkko@kernel.org>,
	Jeff Dike <jdike@addtoit.com>, Kees Cook <keescook@chromium.org>,
	Mark Brown <broonie@kernel.org>,
	Matti Vaittinen <matti.vaittinen@fi.rohmeurope.com>,
	Nick Terrell <terrelln@fb.com>,
	Palmer Dabbelt <palmerdabbelt@google.com>,
	Rasmus Villemoes <linux@rasmusvillemoes.dk>,
	Richard Weinberger <richard@nod.at>,
	Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
	Thomas Gleixner <tglx@linutronix.de>,
	Vasily Gorbik <gor@linux.ibm.com>,
	Vijayanand Jitta <vjitta@codeaurora.org>,
	Vineet Gupta <vgupta@synopsys.com>, Will Deacon <will@kernel.org>,
	Yogesh Lal <ylal@codeaurora.org>
Subject: Re: [PATCH] all: remove GENERIC_FIND_FIRST_BIT
Date: Tue, 11 May 2021 13:53:22 +0000	[thread overview]
Message-ID: <20210511134551.18721-1-alobakin@pm.me> (raw)
In-Reply-To: <20210510233421.18684-1-yury.norov@gmail.com>

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@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@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