Message-ID: <CAErSpo5M9g9UyW_Xc4EtPg-vWf1fOHF+KoSFkmYScXSvi9h5_w@mail.gmail.com>
Date:	Tue, 8 May 2012 09:02:09 -0700
From:	Bjorn Helgaas <bhelgaas@...gle.com>
To:	Andreas Herrmann <andreas.herrmann3@....com>
Cc:	linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
	Ingo Molnar <mingo@...nel.org>, Yinghai Lu <yinghai@...nel.org>
Subject: Re: [PATCH 1/2][RESEND] x86/pci/amd: Restore early_fill_mp_bus_to_node

On Tue, May 8, 2012 at 12:43 AM, Andreas Herrmann
<andreas.herrmann3@....com> wrote:
> On Mon, May 07, 2012 at 09:44:16AM -0700, Bjorn Helgaas wrote:
>> On Mon, May 7, 2012 at 12:35 AM, Andreas Herrmann
>> <andreas.herrmann3@....com> wrote:
>> > On Fri, May 04, 2012 at 10:35:05AM -0600, Bjorn Helgaas wrote:
>> >> On Fri, May 4, 2012 at 7:03 AM, Andreas Herrmann
>> >> <andreas.herrmann3@....com> wrote:
>> >> > On Wed, May 02, 2012 at 11:33:17AM -0600, Bjorn Helgaas wrote:
>> >> >> On Fri, Apr 27, 2012 at 8:36 AM, Andreas Herrmann
>> >> >> <andreas.herrmann3@....com> wrote:
>> >> >> >
>> >> >> > Once upon a time this function was overloaded with quirky stuff to fix
>> >> >> > resource detection on systems w/ _CRS defects (seems that some Sun and
>> >> >> > HP systems were affected).
>> >> >> >
>> >> >> > See commit 30a18d6c3f1e774de656ebd8ff219d53e2ba4029
>> >> >> > (x86: multi pci root bus with different io resource range, on 64-bit)
>> >> >> >
>> >> >> > Restore the old function and thus decouple it from the quirk that is
>> >> >> > CPU family specific (e.g. it won't work on AMD family 15h CPUs). BTW,
>> >> >> > I assume that the _CRS stuff is working on current systems.
>> >> >> >
>> >> >> > This is required to properly initilize the numa_node information of
>> >> >> > existing PCI busses and associated devices.
>> >> >>
>> >> >> I applied some of Yinghai's patches that also touch this area.  Can
>> >> >> you refresh these so they apply on top of my "next" branch
>> >> >> (git://git.kernel.org/pub/scm/linux/kernel/git/helgaas/pci.git next)?
>> >> >
>> >> > Arrgh, will adapt my patch and resend it (asap).
>> >> >
>> >> >> Can you also be more specific about what these patches fix?
>> >> >
>> >> >> My understanding is that amd_bus.c (1) sets NUMA info with
>> >> >> set_mp_bus_to_node() and (2) figures out MMIO and I/O port apertures,
>> >> >> which are only used when blind probing and when ignoring _CRS.
>> >> >>
>> >> >> It seems like the main change in this patch is that we skip (2)
>> >> >> completely when family >= 0x11, and I don't understand what that could
>> >> >> fix.
>> >> >
>> >> > The patch restores a very old function that was used to detect the
>> >> > nearest node for a PCI bus, so yes it's used to do (1). IMHO this
>> >> > function was totally screwed up with Yinghai's code to do (2). It
>> >> > seems that Sun has (had?) some systems where (2) was req'd. I don't
>> >> > care about this part. But I'd like to do (1) on all AMD CPU NUMA
>> >> > systems.
>> >>
>> >> Thanks for the explanation.  But I'm afraid I'm still confused.
>> >>
>> >> First, it sounds like you're trying to change the way we do part (1),
>> >> i.e., the set_mp_bus_to_node() calls, but I think the effect of your
>> >> patch is to stop doing part (2) in some cases.
>> >>
>> >> Second, I am pretty sure that the current early_fill_mp_bus_info()
>> >> (before your patch) does the exact same set_mp_bus_to_node() calls as
>> >> your early_fill_mp_bus_to_node() does.
>> >
>> >
>> > I want to do (1) on all AMD CPUs that might be used in NUMA systems.
>> >
>> > What's done for (2) is very specific to certain AMD CPU families --
>> > some of the register accesses are wrong/incomplete for newer AMD
>> > CPUs. Furhtermore _CRS should provide the required info. I really
>> > don't want to extend all the quirky stuff in (2) for future AMD CPUs.
>>
>> I'm all in favor of limiting part (2) to older AMD CPUs.  I certainly
>> don't want to maintain it for future CPUs.
>>
>> >> Finally, on all systems with ACPI, the set_mp_bus_to_node() call in
>> >> pci_acpi_scan_root() should be doing what you need.  In fact, that
>> >> call happens later, so it should be overwriting the information filled
>> >> in by amd_bus.c.  If there's something wrong in this ACPI path, the
>> >> most likely cause is a BIOS defect, such as  a missing _PXM method on
>> >> the PNP0A03/0A08 host bridge device.
>> >
>> > Good point. I'll check what's wrong in this ACPI path.
>>
>> I hope you find something, especially if it's a bug in the Linux code
>> that interprets  the NUMA info.  Then we could fix that and limit both
>> parts to older CPUs.
>
> Simply, there is no _PXM object for the host bridge devices. At least
> on the systems that I checked.
>
> I'll try to find out whether this is sort of "common BIOS practice" on
> AMD boxes and how to avoid that in the future.

_PXM can also be attached to any parent of the host bridge, since
devices default to the domain of their parents.  It looks like
acpi_get_pxm() should already handle that correctly, so I assume these
systems just don't have any _PXM anywhere in the path between the host
bridge and the root.

If these are just old machines with BIOS bugs, I guess I'm OK with
doing a Linux fix along the lines of your patch.  What I don't like is
just silently covering up BIOS bugs in new platforms by keeping this
CPU-specific code when we have a perfectly good generic mechanism for
doing proximity.  That's a maintenance problem, as you pointed out for
the aperture code (part (2)).

Bjorn
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