linux-kernel - Re: [PATCH v5 02/22] cc_platform: Add new attribute to prevent ACPI CPU hotplug

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Date:   Wed, 29 Jun 2022 11:41:22 +1200
From:   Kai Huang <kai.huang@...el.com>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     Igor Mammedov <imammedo@...hat.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        kvm-devel <kvm@...r.kernel.org>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Len Brown <len.brown@...el.com>,
        Tony Luck <tony.luck@...el.com>,
        Rafael Wysocki <rafael.j.wysocki@...el.com>,
        Reinette Chatre <reinette.chatre@...el.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Andi Kleen <ak@...ux.intel.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        isaku.yamahata@...el.com, Tom Lendacky <thomas.lendacky@....com>,
        Tianyu.Lan@...rosoft.com, Randy Dunlap <rdunlap@...radead.org>,
        "Jason A. Donenfeld" <Jason@...c4.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Mark Rutland <mark.rutland@....com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Yue Haibing <yuehaibing@...wei.com>, dongli.zhang@...cle.com
Subject: Re: [PATCH v5 02/22] cc_platform: Add new attribute to prevent ACPI
 CPU hotplug

On Tue, 2022-06-28 at 19:33 +0200, Rafael J. Wysocki wrote:
> > Hi Rafael,
> > 
> > I am not sure I got what you mean by "This will affect initialization, not
> > just
> > hotplug AFAICS", could you elaborate a little bit?  Thanks.
> 
> So acpi_processor_add() is called for CPUs that are already present at
> init time, not just for the hot-added ones.
> 
> One of the things it does is to associate an ACPI companion with the given
> CPU.
> 
> Don't you need that to happen?

You are right.  I did test again and yes it was also called after boot-time
present cpus are up (after smp_init()).  I didn't check this carefully at my
previous test.  Thanks for catching.

-- 
Thanks,
-Kai