Re: XEN0 kernel with options MULTIPROCESSOR

[Manuel Bouyer <bouyer%antioche.eu.org@localhost>]

On Fri, Mar 31, 2006 at 03:16:03PM +0200, Johan Ihren wrote:
> I understand that if I do explicit CPU - domU assignments then the  
> expected thing happens. But what happens if I *don't* to that? I.e.  
> if I have several CPUs and always leave to Xen to to allocation (i.e.  
> "cpu=-1"):
> 
> * will this lead to static or dynamic CPU allocation? I.e. will a  
> particular domU stay locked on a particular CPU or not?

Static

> 
> * if static: how does the allocation occur? round robin? random?

round robin

> 
> My real concern is this: I often have a significant number of domUs  
> (10+). There is also noticable churn, i.e. some domUs are destroyed  
> and new domUs are created. Today all the domUs run on the same CPU,  
> but I'm planning to aquire one or two SMP boxes for this. If  
> allocation is completely static then it would seem that there's a  
> risk of ending up with an "unbalanced" allocation where most domUs  
> run on one CPU thereby possibly defeating most of the benefits of the  
> SMP box.
> 
> Do I need to work around this by tracking CPU allocation and do  
> explicit allocation for load sharing purposes?

Probably. On one of my Xen/SMP system I had to do this for 2 domU. There are
2 domU with heavy CPU usage, and the others with light load. I forced the
heavy loaded domU on 2 different CPUs, and let Xen allocate a CPU for the
others.

-- 
Manuel Bouyer <bouyer%antioche.eu.org@localhost>
     NetBSD: 26 ans d'experience feront toujours la difference
--