linux-kernel - Re: [PATCH 2/4] x86/amd_nb: add support for newer PCI topologies

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Date:   Sat, 3 Nov 2018 00:29:48 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     "Woods, Brian" <Brian.Woods@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        "x86@...nel.org" <x86@...nel.org>,
        Clemens Ladisch <clemens@...isch.de>,
        Jean Delvare <jdelvare@...e.com>,
        Guenter Roeck <linux@...ck-us.net>, Pu Wen <puwen@...on.cn>,
        Jia Zhang <qianyue.zj@...baba-inc.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-hwmon@...r.kernel.org" <linux-hwmon@...r.kernel.org>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>
Subject: Re: [PATCH 2/4] x86/amd_nb: add support for newer PCI topologies

On Fri, Nov 02, 2018 at 02:59:25PM -0500, Bjorn Helgaas wrote:
> This isn't my code, and I'm not really objecting to these changes, but
> from where I sit, the fact that you need this sort of vendor-specific
> topology discovery is a little bit ugly and seems like something of a
> maintenance issue.  You could argue that this is sort of an "AMD CPU
> driver", which is entitled to be device-specific, and that does make
> some sense.

It is a bunch of glue code which enumerates the PCI devices a CPU
has and other in-kernel users can use that instead of doing the
discovery/enumeration themselves.

> But device-specific code is typically packaged as a driver that uses
> driver registration interfaces like acpi_bus_register_driver(),
> pci_register_driver(), etc.  That gives you a consistent structure
> and, more importantly, a framework for dealing with hotplug.  It
> doesn't look like amd_nb.c would deal well with hot-add of CPUs.

If you mean physical hotadd, then that's a non-issue as, AFAIK, AMD
doesn't support that.

Now, TBH I've never tried soft-offlining the cores of a node and then
check whether using the PCI devices of that node would work.

Now, I don't mind this getting converted to a proper PCI driver as long
as it is not a module as it has to be present at all times. Other than
that, I'm a happy camper.

Thx.

-- 
Regards/Gruss,
    Boris.

Good mailing practices for 400: avoid top-posting and trim the reply.