[libvirt] [PATCH 12/12] nodedev: Export NUMA node locality for PCI devices

[Daniel P. Berrange]

On Fri, May 30, 2014 at 10:14:17AM +0100, Daniel P. Berrange wrote:
> On Thu, May 29, 2014 at 10:32:46AM +0200, Michal Privoznik wrote:
> > A PCI device can be associated with a specific NUMA node. Later, when
> > a guest is pinned to one NUMA node the PCI device can be assigned on
> > different NUMA node. This makes DMA transfers travel across nodes and
> > thus results in suboptimal performance. We should expose the NUMA node
> > locality for PCI devices so management applications can make better
> > decisions.
> > 
> > Signed-off-by: Michal Privoznik <mprivozn at redhat.com>
> > ---
> > 
> > Notes:
> >     All the machines I have tried this on had only -1 in the
> >     numa_node file. From the kernel sources it seems that this is the
> >     default, so I'm not printing the <numa/> element into the XML in
> >     this case. But I'd like to hear your opinion.
> 
> Yes, I believe '-1' means that there is no NUMA locality info
> available for the device, so it makes sense to skip this.

Confirmed in the kernel source 

  include/linux/numa.h:#define    NUMA_NO_NODE    (-1)

Is used when the ACPI tables don't specify any NUMA node for the
PCI device, or when the NUMA node is not online.

Regards,
Daniel
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