RE: [Xen-users] What means "...up to 32-way SMP guest operating systems"

["Petersson, Mats" <Mats.Petersson@xxxxxxx>]

> -----Original Message-----
> From: xen-users-bounces@xxxxxxxxxxxxxxxxxxx 
> [mailto:xen-users-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of 
> Denny Schierz
> Sent: 03 May 2007 11:14
> To: 'xen-users@xxxxxxxxxxxxxxxxxxx'
> Subject: Re: [Xen-users] What means "...up to 32-way SMP 
> guest operating systems"
> 
> hi,
> 
> Guillaume Lenoir schrieb:
> > up to 32 Virtual CPUs in a VM I'd assume ? 
> 
> i assume it too, but does it mean, i need 'bout 32 "physical" CPUs for
> using them inside the VM, or can i "split" a single physical CPU into
> 32CPUs inside the VM?

You can in theory have 32 VCPU's per domain, and you really only need a
single CPU to run say, 8 domains x 32 VCPUs -> 256 VCPUs. Of course,
this isn't a very efficient way to do things. There are some
circumstances where you may want to have a guest run more than 1.0 VCPU
per PCPU (note that it's a "non-integer" number, so you could run 1.3333
VCPU's per PCPU by having 4VCPU, 3PCPU), but that's special cases,
rather than the common scenario. 

Having a total count of VCPU's > PCPU's is quite common however - in
server consolidation, this is exactly what you're looking for.

Finally, the number of physical CPU's Xen can handle is limited by the
bitsize of a "long", which is 32 for 32-bit builds of Xen, whilst in
theory it can be changed to 64 for a 64-bit build. And we're talking CPU
cores here, so with quad-core CPUs, you need 8 sockets to make a 32 CPU
machine. Not exactly the most common variety of motherboard/system. 

--
Mats
> 
> cu denny
> 
> 



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