linux-kernel - Re: [PATCH] ACPI: processor_idle: Skip dummy wait for processors based on the Zen microarchitecture

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Date:   Thu, 22 Sep 2022 09:36:05 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Borislav Petkov <bp@...en8.de>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        K Prateek Nayak <kprateek.nayak@....com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Len Brown <lenb@...nel.org>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>, andi@...as.de,
        Pu Wen <puwen@...on.cn>,
        Mario Limonciello <mario.limonciello@....com>,
        "Zhang, Rui" <rui.zhang@...el.com>,
        "Guilherme G. Piccoli" <gpiccoli@...lia.com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        ananth.narayan@....com, gautham.shenoy@....com,
        Calvin Ong <calvin.ong@....com>,
        Stable <stable@...r.kernel.org>, regressions@...ts.linux.dev
Subject: Re: [PATCH] ACPI: processor_idle: Skip dummy wait for processors
 based on the Zen microarchitecture

On 9/22/22 08:53, Rafael J. Wysocki wrote:
> On Thu, Sep 22, 2022 at 5:36 PM Borislav Petkov <bp@...en8.de> wrote:
>> On Thu, Sep 22, 2022 at 05:21:21PM +0200, Rafael J. Wysocki wrote:
>>> Well, it can be forced to use ACPI idle instead.
>> Yeah, I did that earlier. The dummy IO read in question costs ~3K on
>> average on my Coffeelake box here.
> Well, that's the cost of forcing something non-default.

Just to be clear: The _original_ AMD Zen problem that this thread is
addressing is from a *default* configuration, right?  It isn't that
someone overrode the idle defaults?