linux-kernel - Re: [PATCH 2/5] x86_64, -march=native: POPCNT support

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Message-ID: <20190722211210.GN6698@worktop.programming.kicks-ass.net>
Date:   Mon, 22 Jul 2019 23:12:10 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Alexey Dobriyan <adobriyan@...il.com>
Cc:     tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, hpa@...or.com,
        linux-kernel@...r.kernel.org, x86@...nel.org,
        linux-kbuild@...r.kernel.org, yamada.masahiro@...ionext.com,
        michal.lkml@...kovi.net
Subject: Re: [PATCH 2/5] x86_64, -march=native: POPCNT support

On Mon, Jul 22, 2019 at 11:27:20PM +0300, Alexey Dobriyan wrote:
> Detect POPCNT instruction support and inline hweigth*() functions
> if it is supported by CPU.
> 
> Detect POPCNT at boot time and conditionally refuse to boot.
> 
> Signed-off-by: Alexey Dobriyan <adobriyan@...il.com>
> ---
>  arch/x86/include/asm/arch_hweight.h           | 24 +++++++++++++++++++
>  arch/x86/include/asm/segment.h                |  1 +
>  arch/x86/kernel/verify_cpu.S                  |  8 +++++++
>  arch/x86/lib/Makefile                         |  5 +++-
>  .../drm/i915/display/intel_display_power.c    |  2 +-
>  drivers/misc/sgi-gru/grumain.c                |  2 +-
>  fs/btrfs/tree-checker.c                       |  4 ++--
>  include/linux/bitops.h                        |  2 ++
>  lib/Makefile                                  |  2 ++
>  scripts/kconfig/cpuid.c                       |  7 ++++++
>  scripts/march-native.sh                       |  2 ++
>  11 files changed, 54 insertions(+), 5 deletions(-)

*WHY* ?

AFAICT this just adds lines and complexity and wins aboslutely nothing.