linux-kernel - Re: [PATCH 1/3] acpi/processor: fix evaluating

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Date:   Tue, 29 Nov 2022 09:43:53 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     Roger Pau Monne <roger.pau@...rix.com>,
        linux-kernel@...r.kernel.org
Cc:     xen-devel@...ts.xenproject.org, jgross@...e.com,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Len Brown <lenb@...nel.org>, Alex Chiang <achiang@...com>,
        Venkatesh Pallipadi <venkatesh.pallipadi@...el.com>,
        linux-acpi@...r.kernel.org
Subject: Re: [PATCH 1/3] acpi/processor: fix evaluating _PDC method when
 running as Xen dom0

On 11/21/22 02:21, Roger Pau Monne wrote:
> When running as a Xen dom0 the number of CPUs available to Linux can
> be different from the number of CPUs present on the system, but in
> order to properly fetch processor performance related data _PDC must
> be executed on all the physical CPUs online on the system.

How is the number of CPUs available to Linux different?

Is this a result of the ACPI tables that dom0 sees being "wrong"?

> The current checks in processor_physically_present() result in some
> processor objects not getting their _PDC methods evaluated when Linux
> is running as Xen dom0.  Fix this by introducing a custom function to
> use when running as Xen dom0 in order to check whether a processor
> object matches a CPU that's online.

What is the end user visible effect of this problem and of the solution?