[PATCH RFC 0/5] powerpc:numa Add serial nid support

Nishanth Aravamudan nacc at linux.vnet.ibm.com
Tue Sep 29 03:34:34 AEST 2015

On 27.09.2015 [23:59:08 +0530], Raghavendra K T wrote:
> Problem description:
> Powerpc has sparse node numbering, i.e. on a 4 node system nodes are
> numbered (possibly) as 0,1,16,17. At a lower level, we map the chipid
> got from device tree is naturally mapped (directly) to nid.

chipid is a OPAL concept, I believe, and not documented in PAPR... How
does this work under PowerVM?

> Potential side effect of that is:
> 1) There are several places in kernel that assumes serial node numbering.
> and memory allocations assume that all the nodes from 0-(highest nid)
> exist inturn ending up allocating memory for the nodes that does not exist.
> 2) For virtualization use cases (such as qemu, libvirt, openstack), mapping
> sparse nid of the host system to contiguous nids of guest (numa affinity,
> placement) could be a challenge.
> Possible Solutions:
> 1) Handling the memory allocations is kernel case by case: Though in some
> cases it is easy to achieve, some cases may be intrusive/not trivial. 
> at the end it does not handle side effect (2) above.
> 2) Map the sparse chipid got from device tree to a serial nid at kernel
> level (The idea proposed in this series).
> Pro: It is more natural to handle at kernel level than at lower (OPAL) layer.
> con: The chipid is in device tree no longer the same as nid in kernel

Is there any debugging/logging? Looks like not -- so how does a sysadmin
map from firmware-provided values to the Linux values? That's going to
make debugging of large systems (PowerVM or otherwise) less than
pleasant, it seems? Possibly you could put something in sysfs?


More information about the Linuxppc-dev mailing list