Re: [PATCH] all: remove GENERIC_FIND_FIRST_BIT

From: Alexander Lobakin
Date: Tue May 11 2021 - 09:53:37 EST


From: Yury Norov <yury.norov@xxxxxxxxx>
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@xxxxxxxxx/
>
> 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@xxxxxxxxx>
> ---
> arch/arc/Kconfig | 1 -
> arch/arm64/Kconfig | 1 -
> arch/mips/Kconfig | 1 -

MIPS bit:

Reviewed-by: Alexander Lobakin <alobakin@xxxxx>
Tested-by: Alexander Lobakin <alobakin@xxxxx>

> 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