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Message-ID: <cecd13f6-6d46-4a88-a30b-ce244d8fcd80@citrix.com>
Date:   Fri, 27 Oct 2023 15:12:45 +0100
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From:   Andrew Cooper <andrew.cooper3@citrix.com>
Subject: Re: [PATCH v3 1/6] x86/bugs: Add asm helpers for executing VERW
Content-Language: en-GB
To:     Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Cc:     Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>, x86@kernel.org,
        "H. Peter Anvin" <hpa@zytor.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Josh Poimboeuf <jpoimboe@kernel.org>,
        Andy Lutomirski <luto@kernel.org>,
        Jonathan Corbet <corbet@lwn.net>,
        Sean Christopherson <seanjc@google.com>,
        Paolo Bonzini <pbonzini@redhat.com>, tony.luck@intel.com,
        ak@linux.intel.com, tim.c.chen@linux.intel.com,
        linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org,
        kvm@vger.kernel.org,
        Alyssa Milburn <alyssa.milburn@linux.intel.com>,
        Daniel Sneddon <daniel.sneddon@linux.intel.com>,
        antonio.gomez.iglesias@linux.intel.com,
        Alyssa Milburn <alyssa.milburn@intel.com>
References: <20231025-delay-verw-v3-0-52663677ee35@linux.intel.com>
 <20231025-delay-verw-v3-1-52663677ee35@linux.intel.com>
 <8b6d857f-cbf6-4969-8285-f90254bdafc0@citrix.com>
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In-Reply-To: <20231027134829.7ehdjwf5pfcqr6xp@desk>
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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