RE: [Xen-users] SMP and Memory Limits

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

> -----Original Message-----
> From: Gordan Bobic [mailto:gordan@xxxxxxxxxx] 
> Sent: 20 September 2005 12:34
> To: Petersson, Mats
> Subject: Re: [Xen-users] SMP and Memory Limits
> 
> >>What are the limits on how many CPUs and how much memory 
> Xen supports? 
> >>I am interested in this for both the host (0) kernel and the client 
> >>(U) kernel.
> >>
> >>I am looking at getting some 16-way (8-way dual-core) 
> Opteron systems 
> >>with about 64 GB of RAM for prototyping, so I would like to 
> make sure 
> >>that Xen can use up all of the resources of such a machine.
> > 
> > 
> > In Xen-unstable (to become 3.0) I believe there is no 
> software limits
> > for CPU count or memory amount, only whatever limits the hardware
> > dictates (i.e. 40 bits of hardware address, 48 bits 
> available in virtual
> > space). If there are any other limitations, it's probably fair to
> > consider it a bug, and report such failings on the Xen-Devel mailing
> > list. 
> > 
> > Obviously, 2.0.x, only supporting 32-bit in non-PAE mode 
> would not be
> > able to use more than about 3.5GB of RAM.
> 
> Is that 3.5 GB per dom-U/dom-0, or the total between dom-0 and all 
> dom-Us put together?

That would be 3.5 GB in total, since the only way to access more than
this amount of memory would involve using address extended page table,
which isn't supported by Xen 2.0.x. 64-bit x86 actually uses the
exisiting PAE, but with an added page-table level so that a bigger than
36-bit address can be supported. 
> 
> > Processor count I'm not sure
> > of, but I would think that it would be capable of running on 16
> > processors... 
> 
> OK, thanks.
> 
> Did you send that only to me and not the list deliberately, 
> or accidentally?

It was meant to go to everyone, but for some reason I selected the wrong
button when clicking reply... :-(

--
Mats
> 
> Gordan
> 


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