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

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Date:   Fri, 23 Sep 2022 17:17:35 +0530
From:   Ananth Narayan <ananth.narayan@....com>
To:     "Limonciello, Mario" <Mario.Limonciello@....com>,
        Dave Hansen <dave.hansen@...el.com>,
        "Nayak, K Prateek" <KPrateek.Nayak@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Cc:     "rafael@...nel.org" <rafael@...nel.org>,
        "lenb@...nel.org" <lenb@...nel.org>,
        "linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        "bp@...en8.de" <bp@...en8.de>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "andi@...as.de" <andi@...as.de>, "puwen@...on.cn" <puwen@...on.cn>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "rui.zhang@...el.com" <rui.zhang@...el.com>,
        "gpiccoli@...lia.com" <gpiccoli@...lia.com>,
        "daniel.lezcano@...aro.org" <daniel.lezcano@...aro.org>,
        "Shenoy, Gautham Ranjal" <gautham.shenoy@....com>,
        "Ong, Calvin" <Calvin.Ong@....com>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        "regressions@...ts.linux.dev" <regressions@...ts.linux.dev>
Subject: Re: [PATCH] ACPI: processor_idle: Skip dummy wait for processors
 based on the Zen microarchitecture

On 22-09-2022 11:58 pm, Limonciello, Mario wrote:
>> BTW, is there seriously a strong technical reason that AMD systems are
>> still using this code?  Or is it pure inertia?
> 
> Maybe a better question for Ananth and Prateek to comment on.

We have evaluated using MWAIT for C2 entry and feel that there are good micro
architectural reasons to stick to IOPORT based transitions for now.

Regards,
Ananth