Re: [Xen-users] 2 DomU and 2 4-cores CPU

[peter_booth@xxxxxx]

The question you ask is a multidimensional optimization of a function  
that has discontinuities and depends on both the nature of workloads  
and the specifics of the CPUs.
What specific  CPUs are you referring to?
Basic rule:
1. Dedicate a single core to dom0
(a core meaning real core not a hyperthread path that looks like a  
core to an OS).
2. Limit dom0 to 512mb or less memory

That's it.

Anything else is likely talk and theorizing that is simply wasting  
air. Far better to deploy your rotliafs and start testing. I'll be  
amazed if  configuration of the credit scheduler has a substantive   
impact at this point.
Peter


Sent from my iPhone

On Apr 9, 2010, at 3:27 AM, Michael Schmidt  
<michael.schmidt@xxxxxxxxxx> wrote:
> Hi,
>
> Xen has different CPU schedulers. The default is the credit  
> scheduler - this is a "fair" scheduler.
> Here cou can read more about it:
>
> http://wiki.xensource.com/xenwiki/CreditScheduler
>
> Mit freundlichen Gruessen / Best Regards
>
> Michael SchmidtAm 09.04.10 09:09, schrieb L.M.J:
>
> > On Fri, 02 Apr 2010 10:29:53 +0200, Michael Schmidt
> > <michael.schmidt@xxxxxxxxxx>  wrote:
> >
> > > Hi,
> > >
> > > you can assign all DomUs all cores.
> > > In the case of 100% utilization of both DomUs, the xen-scheduler
> > > provides 50% CPU time from all the CPUs for each DomU.
> > > If one DomU idles and the other one, need 100% CPU, it will get the
> > > power of all the 8 Cores.
> > Thanks Michael for your fast reply. I would like to share what I've  
> > heard
> > from Vmware : when you assigned 4 CPU to a VM, Vmware wait to have  
> > 4 cores
> > free at the same time before give them to the VM which could slow  
> > down your
> > VM instead of speed up.
> > Is there the same issue with Xen ?
> >
> >
> >
> > > L.M.J schrieb:
> > >
> > > > Hi,
> > > >
> > > >   With my college, I was wondering what is the best optimization  
> > > > for our
> > > > setup. I've got 2 VM with 16GB of RAM and 4 vCPU to each one. My  
> > > > server
> > > > got 2 CPU with 4 cores inside (makes 8 CPU). What produce the best
> > > > performance :
> > > >   1) Give ALL cpu to my 2 VM and each ones will take its 4 vCPU  
> > > > where it
> > can
> >
> > > >   2) Give CPU 0-3 to VM1 and CPU 4-7 to VM2 : each vm own the 4  
> > > > cores
> > from 1 CPU
> >
> > > >   3) Give CPU 0,1,4,5 to VM1 and 2,3,6,7 to VM2 : mix cores   
> > > > between the
> > both CPU
> >
> > > >   Thanks by advance for any information or point me to any docs  
> > > > talking
> > about this !
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