[SATLUG] Quad-Core Xeon Server & Linux questions

jaret jaret at aberlorn.com
Fri Sep 25 20:29:04 CDT 2009

I've enjoyed my i7 quad-core and take advantage of the multi-core 
processor by way of virtual machines. I use KVM-libvirt on Ubuntu 9.04 
server with hyperthreading enabled.  I found that if one VM is set to 
use 2 vcpus (virtual cpus = processors), then the VM response is slow. I 
found if I run multiple VMs on a single vcpu, then the VM is slow. 
Ideally I discovered if I run multiple VMs each on a single vcpu, then 
response appears normal. To find out how many vcpus your processor 
supports, from a terminal do "cat /proc/cpuinfo".  The output contains 
groupings by processor number. For example, my i7 with hyperthreading 
enabled, has 8 processors (the output shows them listed as processor 0, 
then 1, then 2... to 7, for a total of 8).

Anyway, in order for the VM to take advantage of the different 
processor, I had to specifically tell the VM to use processor 1 (or 2 or 
3, etc) in the libvirt configuration file. I think Xen employs a similar 

Sorry, David, but I've only played a little bit with speed and not 
exactly sure what kind of software to use to test response times or get 
at more detailed multi-core processing rates. (If you have particular 
ideas to test performance, I'd love to know.)


David Salisbury wrote:
> Considering throwing together a box with a quad-core Xeon at the helm, 
> and was wondering what general experiences were with multi-core 
> processors and some of the newer distros?  I think with SMP-enabled 
> kernels most of the distros will take advantage of all of the 
> available cores, is that correct?  What about software packages?  I 
> guess those would be on a per-software basis as to whether or not they 
> use the cores?  I'm thinking of SAMBA, for one.  Anyway, glad to hear 
> whatever anyone's experiences are!  Thanks!
> David

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