Hi,

On Friday 11 January 2013 15:11:45 vbox-users wrote:
> > From: Michael Da Cova [mailto:[email protected]]
> > 
> > up-to now I have been running VB on dual core ubuntu hosts and for some
> > reason I have it in my head that clients run better if all clients cpu
> > match the host in this case two. what do people think is this right. I
> > now have a i3 server and it gives me 4 cpu's should I maintain my policy
> > of always matching the numbers of cpu's
> 
> Guests benefit by having more than one cpu.  If more than one guest is
> competing for CPU, they load balance.  So generally speaking I think it's
> a good idea to give all of your CPU's to all of your guests.  Well...  n-1
> 
> If I *actually* give all the cpu's to all the guests, there doesn't seem to
> be enough leftover for the host to figure out the load balancing very
> well.  So I generally assign n-1 to each guest.
> 
> The big question is hyperthreading.  If you have 4 cores that virtually
> look like 8, how do you count that?  Do you think you have 4?  Or 8?  I've
> never come up with an answer to this question, so I take the conservative
> approach.

You should count physical cores on the host, not hyperthreads. And do only
enable multiple processors in the guest if this is really necessary
(e.g. your guest does CPU-intensive tasks). A normal webserver is often
happy with a single core. Enabling multiprocessor support in the guest
induces more overhead for synchronization.

Kind regards,

Frank
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