linux-kernel - Re: [PATCH v3 06/12] x86/amd_nb: Use topology info to get AMD node count

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Message-ID: <20251023190901.GA840389@yaz-khff2.amd.com>
Date: Thu, 23 Oct 2025 15:09:01 -0400
From: Yazen Ghannam <yazen.ghannam@....com>
To: Michal Pecio <michal.pecio@...il.com>
Cc: Shyam-sundar.S-k@....com, bhelgaas@...gle.com, hdegoede@...hat.com,
	ilpo.jarvinen@...ux.intel.com, jdelvare@...e.com,
	linux-edac@...r.kernel.org, linux-hwmon@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
	linux@...ck-us.net, mario.limonciello@....com,
	naveenkrishna.chatradhi@....com,
	platform-driver-x86@...r.kernel.org, suma.hegde@....com,
	tony.luck@...el.com, x86@...nel.org
Subject: Re: [PATCH v3 06/12] x86/amd_nb: Use topology info to get AMD node
 count

On Thu, Oct 23, 2025 at 03:04:29PM -0400, Yazen Ghannam wrote:
> On Thu, Oct 23, 2025 at 08:25:03PM +0200, Michal Pecio wrote:
> > On Thu, 23 Oct 2025 12:09:06 -0400, Yazen Ghannam wrote:
> > > The kernel seems to think there are 6 CPUs on your system:
> > > 
> > > [    0.072059] CPU topo: Allowing 4 present CPUs plus 2 hotplug CPUs
> > 
> > I wonder if this code doesn't break systems which actually support
> > hotplug, when some sockets aren't populated at boot?
> 
> I don't know about other vendors, but we don't do physical CPU hotplug.
> CPU hotplug, in this case, is there are physical CPUs already in the
> system, but they are not enabled for whatever policy decision. They
> could be disabled in BIOS, and so the MADT entries will reflect that. Or
> they can be disabled by kernel parameters.
> 

Sorry for the rapid emails. Here's another interesting commit:
f0551af02130 ("x86/topology: Ignore non-present APIC IDs in a present package")

Thanks,
Yazen