Re: [PATCH] Fix northbridge quirk to assign correct NUMA node

[Bjorn Helgaas]

[+cc linux-pci, Myron, Suravee, Kim, Aravind]

On Thu, Mar 13, 2014 at 5:43 AM, Daniel J Blueman <daniel@xxxxxxxxxxxxx> wrote:
> For systems with multiple servers and routed fabric, all northbridges get
> assigned to the first server. Fix this by also using the node reported from
> the PCI bus. For single-fabric systems, the northbriges are on PCI bus 0
> by definition, which are on NUMA node 0 by definition, so this is invarient
> on most systems.
>
> Tested on fam10h and fam15h single and multi-fabric systems and candidate
> for stable.

I wish this had been cc'd to linux-pci.  We're talking about a related
change by Suravee there.  In fact, we were hoping this quirk could be
removed altogether.

I don't understand what this quirk is doing.  Normally we discover the
NUMA node for a PCI host bridge via the ACPI _PXM method.  The way
_PXM works is that every PCI device in the hierarchy below the bridge
inherits the same node number as the host bridge.  I first thought
this might be a workaround for a system that lacks _PXM, but I don't
think that can be right, because you're only changing the node for a
few devices, not the whole hierarchy.

So I suspect the problem is more complicated, and maybe _PXM is
insufficient to describe the topology?  Are there subtrees that should
have nodes different from the host bridge?

I know this patch is already in v3.14-rc7, but I'd still like to
understand it so we can do the right thing with Suravee's patch.

Bjorn

> Signed-off-by: Daniel J Blueman <daniel@xxxxxxxxxxxxx>
> Acked-by: Steffen Persvold <sp@xxxxxxxxxxxxx>
> ---
>  arch/x86/kernel/quirks.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/kernel/quirks.c b/arch/x86/kernel/quirks.c
> index 04ee1e2..52dbf1e 100644
> --- a/arch/x86/kernel/quirks.c
> +++ b/arch/x86/kernel/quirks.c
> @@ -529,7 +529,7 @@ static void quirk_amd_nb_node(struct pci_dev *dev)
>                 return;
>
>         pci_read_config_dword(nb_ht, 0x60, &val);
> -       node = val & 7;
> +       node = pcibus_to_node(dev->bus) | (val & 7);
>         /*
>          * Some hardware may return an invalid node ID,
>          * so check it first:
> --
> 1.8.3.2
>
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