linux-kernel - Re: [PATCHv14 08/17] x86/mm: Reduce untagged_addr() overhead until the first LAM user

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Message-ID: <Y8bnHnLe2a+vzHDd@hirez.programming.kicks-ass.net>
Date:   Tue, 17 Jan 2023 19:21:18 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>, x86@...nel.org,
        Kostya Serebryany <kcc@...gle.com>,
        Andrey Ryabinin <ryabinin.a.a@...il.com>,
        Andrey Konovalov <andreyknvl@...il.com>,
        Alexander Potapenko <glider@...gle.com>,
        Taras Madan <tarasmadan@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        "H . J . Lu" <hjl.tools@...il.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Rick Edgecombe <rick.p.edgecombe@...el.com>,
        Bharata B Rao <bharata@....com>,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        Ashok Raj <ashok.raj@...el.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        Sami Tolvanen <samitolvanen@...gle.com>,
        ndesaulniers@...gle.com, joao@...rdrivepizza.com
Subject: Re: [PATCHv14 08/17] x86/mm: Reduce untagged_addr() overhead until
 the first LAM user

On Tue, Jan 17, 2023 at 09:18:01AM -0800, Linus Torvalds wrote:

> But maybe even those aren't worth worrying about. At least they do the
> unmasking outside the loop - although then in the case of execve(),
> the string copies themselves are obviously done in a loop anyway.
> 
> Kirill, do you have clear numbers for that static key being a noticeable win?

Numbers would be good; I think this all started as a precaution, but
clearly that's not really working out so well :/