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Re: [Xen-users] SMP and Memory Limits

To: xen-users@xxxxxxxxxxxxxxxxxxx
Subject: Re: [Xen-users] SMP and Memory Limits
From: Gordan Bobic <gordan@xxxxxxxxxx>
Date: Tue, 20 Sep 2005 14:26:33 +0100
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Petersson, Mats wrote:
-----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.

How stable is the "unstable/64-bit" version of Xen? Is it usable?

Gordan

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