[vbox-dev] CPU detection problem

Klaus Espenlaub klaus.espenlaub at oracle.com
Thu Jan 30 19:17:53 UTC 2014

Hi Laura,

On 30.01.2014 16:55, Baxter, Laura wrote:
> Hi,
> I'm running VirtualBox version 4.3.6 r91406.
> The basic problem I am having is that although my (Linux) server has 
> 64 CPUs, (4 nodes each with 16 CPUs/8cores with 2 threads per core), 
> my VM is only allowing me to set 8 processors (max).
VirtualBox can definitely deal with multi-socket systems (has been 
tested on 8 socket systems with 10 cores with 2 threads per core), so we 
need to get a bit more detail about the reality (the output of "cat 
/dev/cpuinfo") and what VirtualBox thinks (the output of "VBoxManage 
list hostinfo"), as the combination will give us a lot of hints what 
information might be wrong. lscpu is a very useful command to get a 
quick overview, but we need the lower level details. Actually the lscpu 
output you provided somewhat contradicts your claims above, you have a 
system with 8 nodes with 8 cores each - AMD doesn't do hyperthreading.
> My question is, how can i get my VM to "see" all 64 nodes, to increase 
> the VM's processing power?
Careful with the assumption "more VCPUs = faster VM" - even if the 
workload on real hardware scales very well, it might be different in a 
VM, as the I/O overhead is much higher, and the cross-VCPU 
synchronization can be extremely expensive.
> Is this an issue with NUMA not being supported/implemented?
NUMA as such isn't supported (as far as optimizing memory placement is 
concerned), but VirtualBox should definitely be able to use all CPUs and 
the entire memory.
> Below are some details of the VM and the server, I hope someone has 
> some ideas to help, i wonder if this issue affects other users?
We should be able to figure out what's going on... it's definitely not 
affecting everyone (and as you're using Linux it's definitely not the 
issue that modern Windows versions pretend that AMD does hyperthreading, 
assuming that the CPUs in the systems are actually threads, and that the 
core count is half the thread count).

> Many thanks,
> Laura
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