[libvirt] [PATCH] nodeinfo: Add workaround if kernel reports bogous numa topology.

[Peter Krempa]

On 10/23/12 17:07, Eric Blake wrote:
> On 10/23/2012 06:40 AM, Peter Krempa wrote:
>> This patch adds a workaround for the cpu topology detection code if the
>> kernel reports incorrect count of numa nodes or any other reason that
>> might result in duplicate core ID's in one socket.
>
> Do we know what versions of kernels have this bug?  If it is still
> current, has this been opened as a bug report against the kernel?

The kernel version this happens in is 3.5.3-1.fc17.x86_64. You need a 
two socket AMD magny-cours machine. The problem might be that the kernel 
doesn't know about the topology due to hardware issues (not yet known)

[...]

>
> If you install the 'hwloc' package on the afflicted machine, can you
> then send us the file created by  'lstopo proc.png', so we can get a
> better feel for what the machine actually supports?  Is it really a case
> of duplicate processor ids being mistakenly reported by the kernel, or
> more a case of us mis-reading sysfs and seeing duplicates because we
> aren't looking in enough other places?
>
> At any rate, this patch looks okay, if we can prove that the kernel
> really is giving us bogus information, and not just a case of us
> misreading things.

Forwarding the response from George-Cristian Bîrzan who initialy 
reported that:

George-Cristian has a bunch of identical machines where some report 
having 4 NUMA cells and some just 1:

[...]

I did it on two hosts, one with 1 NUMA cell, one with 4 (as I said before,
they both only report 12 cores though):

http://birzan.org/proc1.png
http://birzan.org/proc4.png

------

I think we should take this patch as it resolves this case. The data 
reported by kernel looks OK and the kernel probably trusts that 
everything is OK.


Peter