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From:   Nick Desaulniers <ndesaulniers@google.com>
Date:   Tue, 17 Aug 2021 11:22:26 -0700
Message-ID: <CAKwvOdk+fwHQDe23Ttva46tyB9yGGxB73zXzNPkcMCggSRWUdQ@mail.gmail.com>
Subject: Re: [PATCH 2/2] x86, Makefile: Add new generic x86-64 settings v2/v3/v4
To:     torvic9@mailbox.org
Cc:     "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "x86@kernel.org" <x86@kernel.org>,
        "clang-built-linux@googlegroups.com" 
        <clang-built-linux@googlegroups.com>,
        "graysky@archlinux.us" <graysky@archlinux.us>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Masahiro Yamada <masahiroy@kernel.org>
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On Tue, Aug 17, 2021 at 11:17 AM Nick Desaulniers
<ndesaulniers@google.com> wrote:
>
> On Tue, Aug 17, 2021 at 7:24 AM torvic9 via Clang Built Linux
> <clang-built-linux@googlegroups.com> wrote:
> >
> > Add new generic x86-64 CPU tunings introduced with recent versions of
> > gcc and clang, as documented in x86-64-psABI [1].
> >
> > This is taken straight from graysky's CPU optimization patch with minor
> > modifications [2].
> >
> > [1] https://gitlab.com/x86-psABIs/x86-64-ABI/-/commit/77566eb03bc6a326811cb7e9a6b9396884b67c7c
> > [2] https://github.com/graysky2/kernel_compiler_patch
> >
> > Signed-off-by: Tor Vic <torvic9@mailbox.org>
> > ---
> >  arch/x86/Kconfig.cpu  | 26 +++++++++++++++++++++++++-
> >  arch/x86/Makefile.cpu |  6 ++++++
> >  2 files changed, 31 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/x86/Kconfig.cpu b/arch/x86/Kconfig.cpu
> > index 814fe0d349b0..a2c872aa5a0b 100644
> > --- a/arch/x86/Kconfig.cpu
> > +++ b/arch/x86/Kconfig.cpu
> > @@ -294,6 +294,30 @@ config GENERIC_CPU
> >           Generic x86-64 CPU.
> >           Run equally well on all x86-64 CPUs.
> >
> > +config GENERIC_CPU_V2
> > +       bool "Generic-x86-64-v2"
> > +       depends on ( CC_IS_GCC && GCC_VERSION > 110000 ) || ( CC_IS_CLANG && CLANG_VERSION >= 120000 )
>
> Can we stick with either > or >=, but at least be consistent? Also,
> there's unnecessary whitespace inside the parens that could be
> removed.

Ah, cc-option can be used from Kconfig. Perhaps a cc-option call to
-march=x86-64-vX with a comment about which compiler versions first
supported these (so that we can remove the feature test when the
minimum supported toolchains are advanced) would be better?

>
> > +       depends on X86_64
> > +       help
> > +         Generic x86-64 CPU.
> > +         Run equally well on all x86-64 CPUs with min support of x86-64-v2.
> > +
> > +config GENERIC_CPU_V3
> > +       bool "Generic-x86-64-v3"
> > +       depends on ( CC_IS_GCC && GCC_VERSION > 110000 ) || ( CC_IS_CLANG && CLANG_VERSION >= 120000 )
> > +       depends on X86_64
> > +       help
> > +         Generic x86-64-v3 CPU with v3 instructions.
> > +         Run equally well on all x86-64 CPUs with min support of x86-64-v3.
> > +
> > +config GENERIC_CPU_V4
> > +       bool "Generic-x86-64-v4"
> > +       depends on ( CC_IS_GCC && GCC_VERSION > 110000 ) || ( CC_IS_CLANG && CLANG_VERSION >= 120000 )
> > +       depends on X86_64
> > +       help
> > +         Generic x86-64 CPU with v4 instructions.
> > +         Run equally well on all x86-64 CPUs with min support of x86-64-v4.
> > +
> >  endchoice
> >
> >  config X86_GENERIC
> > @@ -318,7 +342,7 @@ config X86_INTERNODE_CACHE_SHIFT
> >  config X86_L1_CACHE_SHIFT
> >         int
> >         default "7" if MPENTIUM4 || MPSC
> > -       default "6" if MK7 || MK8 || MPENTIUMM || MCORE2 || MATOM || MVIAC7 || X86_GENERIC || GENERIC_CPU
> > +       default "6" if MK7 || MK8 || MPENTIUMM || MCORE2 || MATOM || MVIAC7 || X86_GENERIC || GENERIC_CPU || GENERIC_CPU_V2 || GENERIC_CPU_V3 || GENERIC_CPU_V4
> >         default "4" if MELAN || M486SX || M486 || MGEODEGX1
> >         default "5" if MWINCHIP3D || MWINCHIPC6 || MCRUSOE || MEFFICEON || MCYRIXIII || MK6 || MPENTIUMIII || MPENTIUMII || M686 || M586MMX || M586TSC || M586 || MVIAC3_2 || MGEODE_LX
> >
> > diff --git a/arch/x86/Makefile.cpu b/arch/x86/Makefile.cpu
> > index fb407ae94d90..f190feefe964 100644
> > --- a/arch/x86/Makefile.cpu
> > +++ b/arch/x86/Makefile.cpu
> > @@ -10,3 +10,9 @@ cflags-$(CONFIG_MCORE2) += \
> >  cflags-$(CONFIG_MATOM) += $(call cc-option,-march=atom) \
> >         $(call cc-option,-mtune=atom,$(call cc-option,-mtune=generic))
> >  cflags-$(CONFIG_GENERIC_CPU) += $(call cc-option,-mtune=generic)
> > +
> > +# New generic x86-64 CPU options.
> > +# Don't call the compiler, we have Kconfig compiler checks for these.
>
> You'd be surprised how quickly using time-relative words like "New"
> bitrot. My copy of "Modern C++" already doesn't feel very "modern" for
> example.  I'd just drop the comment block here; we don't need a
> comment every time we skip cc-option checks.  Thanks for the patches!
>
> > +cflags-$(CONFIG_GENERIC_CPU_V2) += -march=x86-64-v2
> > +cflags-$(CONFIG_GENERIC_CPU_V3) += -march=x86-64-v3
> > +cflags-$(CONFIG_GENERIC_CPU_V4) += -march=x86-64-v4
> > --
> --
> Thanks,
> ~Nick Desaulniers


-- 
Thanks,
~Nick Desaulniers