linux-kernel - Re: [PATCH v3 1/6] x86/bugs: Add asm helpers for executing VERW

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Message-ID: <cecd13f6-6d46-4a88-a30b-ce244d8fcd80@citrix.com>
Date:   Fri, 27 Oct 2023 15:12:45 +0100
From:   Andrew Cooper <andrew.cooper3@...rix.com>
To:     Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Jonathan Corbet <corbet@....net>,
        Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>, tony.luck@...el.com,
        ak@...ux.intel.com, tim.c.chen@...ux.intel.com,
        linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
        kvm@...r.kernel.org,
        Alyssa Milburn <alyssa.milburn@...ux.intel.com>,
        Daniel Sneddon <daniel.sneddon@...ux.intel.com>,
        antonio.gomez.iglesias@...ux.intel.com,
        Alyssa Milburn <alyssa.milburn@...el.com>
Subject: Re: [PATCH v3 1/6] x86/bugs: Add asm helpers for executing VERW

On 27/10/2023 2:48 pm, Pawan Gupta wrote:
> On the bright-side, I am seeing even better perf with VERW operand
> out-of-line:
> 
> Baseline: v6.6-rc5
> 
> | Test               | Configuration          | v1   | v3   |
> | ------------------ | ---------------------- | ---- | ---- |
> | build-linux-kernel | defconfig              | 1.00 | 1.00 |
> | hackbench          | 32 - Process           | 1.02 | 1.06 |
> | nginx              | Short Connection - 500 | 1.01 | 1.04 |
> 
> Disclaimer: These are collected by a stupid dev who knows nothing about
> perf, please take this with a grain of salt.

:)

Almost as if it's a good idea to follow the advice of the Optimisation
Guide on mixing code and data, which is "don't".

~Andrew