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

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Message-ID: <53e6d589-2470-5709-0db0-687ef1f35bf4@amd.com>
Date:   Wed, 21 Sep 2022 14:55:04 -0500
From:   "Limonciello, Mario" <mario.limonciello@....com>
To:     Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...el.com>
Cc:     K Prateek Nayak <kprateek.nayak@....com>,
        linux-kernel@...r.kernel.org, rafael@...nel.org, lenb@...nel.org,
        linux-acpi@...r.kernel.org, linux-pm@...r.kernel.org,
        dave.hansen@...ux.intel.com, tglx@...utronix.de, andi@...as.de,
        puwen@...on.cn, peterz@...radead.org, rui.zhang@...el.com,
        gpiccoli@...lia.com, daniel.lezcano@...aro.org,
        ananth.narayan@....com, gautham.shenoy@....com,
        Calvin Ong <calvin.ong@....com>, 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 9/21/2022 14:51, Borislav Petkov wrote:
> On Wed, Sep 21, 2022 at 07:15:07AM -0700, Dave Hansen wrote:
>> In the end, the delay is because of buggy, circa 2006 chipsets?  So, we
>> use a CPU vendor specific check to approximate that the chipset is
>> recent and not affected by the bug?  If so, is there no better way to
>> check for a newer chipset than this?
> 
> So I did some git archeology but that particular addition is in some
> conglomerate, glued-together patch from 2007 which added the cpuidle
> tree:
> 
> commit 4f86d3a8e297205780cca027e974fd5f81064780
> Author: Len Brown <len.brown@...el.com>
> Date:   Wed Oct 3 18:58:00 2007 -0400
> 
>      cpuidle: consolidate 2.6.22 cpuidle branch into one patch
> 
> 
> so the most precise check here should be to limit that dummy read to
> that Intel chipset which needed it. Damned if I knew how to figure out
> which...
> 

Functionally most Intel platforms use intel_idle though these days 
though, right?