[Xen-devel] RE: A question about changeset 20621:f9392f6eda79 and Discontinuous online node

["Jiang, Yunhong" <yunhong.jiang@xxxxxxxxx>]

>-----Original Message-----
>From: Keir Fraser [mailto:keir.fraser@xxxxxxxxxxxxx]
>Sent: Wednesday, January 06, 2010 4:36 PM
>To: Jiang, Yunhong; andre.przywara@xxxxxxx
>Cc: xen-devel@xxxxxxxxxxxxxxxxxxx
>Subject: Re: A question about changeset 20621:f9392f6eda79 and Discontinuous
>online node
>
>On 06/01/2010 08:14, "Jiang, Yunhong" <yunhong.jiang@xxxxxxxxx> wrote:
>
>> This continuous assumption apply to CPU side also. Currently nr_cpus is
>> returned as num_online_cpus(), this will cause issue if some of cpu is
>> offlined.
>>
>> I'm considering if we can pass this dis-continuous information to user space
>> too, but that requires change this sysctl interface. The worse is, even if we
>> can change this interface, we may run out of the 128 byte limitation for
>> xen_sysctl hypercall if we change the NR_CPUS == 128 in future (currently the
>> struct xen_sysctl_physinfo is 104 byte already).
>>
>> I'd get some input from you guys and community before I try to fix this 
>> issue,
>> any suggestion?
>
>I think sufficient info is already made available by sysctl: cpu_to_node[]
>info is provided by physinfo command; cpu_to_core[] and cpu_to_socket[] by
>get_cputopo command. In both cases holes due to offline cpus are filled with
>a special indicator value of ~0.
>
>In the case of the node_to_cpu list returned by xc.physinfo(), it already
>accounts for holes in node space by having empty lists of cpus for those
>non-existent or empty nodes. Should just be a case of having the xend python
>code understand that as necessary?

Keir, thanks for pointing out this.The API is sufficient. We only need changes 
to python side to understand this. One minor thing is, maybe we need change the 
nr_nodes from number of online node to the maxium of online node id, otherwise, 
xc.physinfo may have no idea when iterate the node_to_memory information (will 
it be possible the a node has only memory populated, while no CPU populated?)

--jyh

>
> -- Keir
>


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