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Re: [libvirt] Problem of host CPU topology parsing



On 11.05.2012 10:40, Osier Yang wrote:
> On 2012年05月11日 16:35, Daniel P. Berrange wrote:
>> On Fri, May 11, 2012 at 04:21:48PM +0800, Osier Yang wrote:
>>> Hi,
>>>
>>> We have problem of host CPU topology parsing on special
>>> platforms (general platforms are fine). E.g.
>>>
>>> On a AMD machine with 48 CPUs [1] (4 sockets, 6 cores indeed
>>> [2]), VIR_NODEINFO_MAXCPUS [3] will always return 24 as the
>>> total CPU number.
>>
>> If it is returning 24, then surely we have the 'nodes' value
>> wrong in the virNodeInfo ? It sounds like it should have been
>> set to 2  (4 * 6 * 2 =>  48)
> 
>     /* nodeinfo->sockets is supposed to be a number of sockets per NUMA
> node,
>      * however if NUMA nodes are not composed of whole sockets, we just lie
>      * about the number of NUMA nodes and force apps to check
> capabilities XML
>      * for the actual NUMA topology.
>      */
>     if (nodeinfo->sockets % nodeinfo->nodes == 0)
>         nodeinfo->sockets /= nodeinfo->nodes;
>     else
>         nodeinfo->nodes = 1;
> 
> Jirka said this was for a fix, but I don't quite understand it,
> what does the "nodeinfo.nodes" mean actually? Shouldn't it
> be 8 (for the 48 CPUs machine) instead? But then we will be
> wrong again with using VIR_NODEINFO_MAXCPUS.

Why do you think it will be wrong? My understanding is that
VIR_NODEINFO_MAXCPUS just tell the max number of possible cpus not the
actual. So if it's over 48 we are safe. Btw: the code above seems like a
hack to me.

Michal


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