linux-kernel - Re: [RFC 0/3] x86: Patchable constants

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Message-ID: <20180207162507.GB25219@hirez.programming.kicks-ass.net>
Date:   Wed, 7 Feb 2018 17:25:07 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>, x86@...nel.org,
        Tom Lendacky <thomas.lendacky@....com>,
        Dave Hansen <dave.hansen@...el.com>,
        Andy Lutomirski <luto@...nel.org>,
        Borislav Petkov <bp@...e.de>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC 0/3] x86: Patchable constants

On Wed, Feb 07, 2018 at 05:59:10PM +0300, Kirill A. Shutemov wrote:
> This conversion makes GCC generate worse code. Conversion __PHYSICAL_MASK
> to a patchable constant adds about 5k in .text on defconfig and makes it
> slightly slower at runtime (~0.2% on my box).

Do you have explicit examples for the worse code? That might give clue
on how to improve things.