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Date:   Thu, 22 Sep 2022 10:17:05 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Borislav Petkov <bp@alien8.de>
Cc:     K Prateek Nayak <kprateek.nayak@amd.com>,
        linux-kernel@vger.kernel.org, rafael@kernel.org, lenb@kernel.org,
        linux-acpi@vger.kernel.org, linux-pm@vger.kernel.org,
        dave.hansen@linux.intel.com, tglx@linutronix.de, andi@lisas.de,
        puwen@hygon.cn, mario.limonciello@amd.com, rui.zhang@intel.com,
        gpiccoli@igalia.com, daniel.lezcano@linaro.org,
        ananth.narayan@amd.com, gautham.shenoy@amd.com,
        Calvin Ong <calvin.ong@amd.com>, stable@vger.kernel.org,
        regressions@lists.linux.dev
Subject: Re: [PATCH] ACPI: processor_idle: Skip dummy wait for processors
 based on the Zen microarchitecture
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References: <20220921063638.2489-1-kprateek.nayak@amd.com>
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On Wed, Sep 21, 2022 at 09:48:13PM +0200, Borislav Petkov wrote:
> On Wed, Sep 21, 2022 at 05:00:35PM +0200, Peter Zijlstra wrote:
> > On Wed, Sep 21, 2022 at 12:06:38PM +0530, K Prateek Nayak wrote:
> > > Processors based on the Zen microarchitecture support IOPORT based deeper
> > > C-states. 
> > 
> > I've just gotta ask; why the heck are you using IO port based idle
> > states in 2022 ?!?! You have have MWAIT, right?
> 
> They have both. And both is Intel technology. And as I'm sure you
> know AMD can't do their own thing - they kinda have to follow Intel.
> Unfortunately.
> 
> Are you saying modern Intel chipsets don't do IO-based C-states anymore?

I've no idea what they do, but Linux exclusively uses MWAIT on Intel as
per intel_idle.c.

MWAIT also cuts down on IPIs because it wakes from the TIF write.