linux-kernel - Re: [PATCH v5 04/13] x86/fsgsbase/64: Add intrinsics for FSGSBASE instructions

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Date:   Fri, 1 Feb 2019 18:52:35 -0800
From:   Andy Lutomirski <luto@...nel.org>
To:     "Chang S. Bae" <chang.seok.bae@...el.com>
Cc:     Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        "H . Peter Anvin" <hpa@...or.com>, Andi Kleen <ak@...ux.intel.com>,
        Markus T Metzger <markus.t.metzger@...el.com>,
        Ravi Shankar <ravi.v.shankar@...el.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 04/13] x86/fsgsbase/64: Add intrinsics for FSGSBASE instructions

On Fri, Feb 1, 2019 at 12:54 PM Chang S. Bae <chang.seok.bae@...el.com> wrote:
>
> From: Andi Kleen <ak@...ux.intel.com>
>
> Add C intrinsics and assembler macros for the new FSBASE and GSBASE
> instructions.
>
> Very straight forward. Used in followon patches.
>
> [ luto: Rename the variables from FS and GS to FSBASE and GSBASE and
>   make <asm/fsgsbase.h> safe to include on 32-bit kernels. ]
>
> v2: Use __always_inline
>
> [ chang: Revise the changelog. Place them in <asm/fsgsbase.h>. Replace
>   the macros with GAS-compatible ones. ]
>
> If GCC supports it, we can add -mfsgsbase to CFLAGS and use the builtins
> here for extra performance

Does it really get better performance?  If so, let's do it.  If not,
let's remove the comment.  And, whatever you do, please put this above
the [luto] and [chang] parts.
.
>
> [ chang: Use FSGSBASE instructions directly. Removed GAS-compatible
>   macros as the minimum required binutils (v2.21) supports the FSGSBASE
>   instructions. ]

Can you stick the "v2" revision notes below the --- or even just
remove them?  It makes the changelog a lot harder to review and it's
not really useful in the git tree.