[SlugBug] Multiprocessor and Xen

[Alan Dawson]

Hi

Quoting Andy Davidson <andy at nosignal.org>:

> 
> My thoughts are either :
>     - I will have to configure a guest to use a specific processor or  
> thread
> or - Xen will balance the work across all processors transparently
> 
> Which is right ?  Anyone have some interesting empirical thoughts ?
> 


Sorry ..  no empirical thoughts .. I've some xen machines running( xen 3.0.1 on
debian sarge ), and I did notice that man xm mentions 

       vcpu-pin domain-id vcpu cpus
           Pins the the VCPU to only run on the specific CPUs.

and there is a section on Scheduler Subcommands, with some examples like

           4 domains with weights 2:3:4:2

               xm sched-sedf <d1> 0 0 0 0 2
              xm sched-sedf <d2> 0 0 0 0 3
              xm sched-sedf <d3> 0 0 0 0 4
              xm sched-sedf <d4> 0 0 0 0 2

So I guess you can assign domain 1 and domain 2 to CPU 1 only with weights 3:2
and domains 3,4,5 to cpu's 2,3,4 with weights 1:1:2  if you need to.

But I found it a little complex, and didn't feel the need to get involved in
setting that much detail.

Where I did find resource sharing conflicts between DomU's was when one decided
to swap, and then generally the disk became a bottleneck across all the DomU's 
Though that machine has just a couple of SATA disks, not particulary hi spec

Also xen enterprise has some tools for setting resource sharing,but i guess that
they are just wrappers to the xm commands.

http://kb.xensource.com/kbcategory.jspa?categoryID=34

hope that helps,

Alan Dawson
-- 
"The long revolution is creating small federated microsocieties, true guerilla
cells practising and fighting for this self-management. Effective radicality
authorises all variations and guarantees every freedom"