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

[Daniel J Blueman]

On 03/22/2014 01:16 AM, Suravee Suthikulpanit wrote:
> On 3/20/2014 10:38 PM, Daniel J Blueman wrote:
> > On 21/03/2014 06:07, Bjorn Helgaas wrote:
> > > [+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.
> >
> > Noted.
> >
> > > 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?
> >
> > Yes; see below.
> >
> > > 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.
> >
> > The _PXM method associates each northbridge with the first NUMA node,
> > 0 in single-fabric systems, and eg 4 for the second server in a
> > multi-fabric system with 2 dual-module Opterons (with 2 NUMA nodes
> > internally) etc, since the northbridges appear in the
> > PCI tree, under the host bridge, not above it [1].
> Daniel,
>
> That lspci looks interesting, what is the value returned from
> pci_bus_to_node() on your system for each fabric?

pci_bus_to_node returns 0 for PCI domain 0000, 2 for PCI domain 0001, 4 
for PCI domain 0002 and so on.

Our processor fabric interconnect has HyperTransport NodeId 2 on each 
server (as they start from bus 0, device 0x18 of course):
0000:00:1a.0 Host bridge: Device 1b47:0601 (rev 02)
0000:00:1a.1 Host bridge: Device 1b47:0602 (rev 02)

Thanks,
  Daniel
--
Daniel J Blueman
Principal Software Engineer, Numascale
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