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Re: [Xen-devel] Supported #of CPUs/VMs per CPUs

To: "Daniel P. Berrange" <berrange@xxxxxxxxxx>
Subject: Re: [Xen-devel] Supported #of CPUs/VMs per CPUs
From: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>
Date: Mon, 18 Sep 2006 13:29:24 +0100
Cc: whit <whitson22@xxxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx
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On 18/9/06 13:17, "Daniel P. Berrange" <berrange@xxxxxxxxxx> wrote:

>> Xen supports up to 32 CPUs on a 32-bit system, or 64 CPUs (by default) on a
>> 64-bit system. Guests can have up to 32 virtual CPUs. The only limit to
>> number of domains is amount of hardware resource (mainly memory) that you
>> have to share.
> Are these hard limits, or just the kernel config defaults for Xen kernels ?
> Any reason the guest VCPU count is limited to less than the physical number
> on x86_64 ? (not that I expect much demand for 64 CPU guests)

All are hard limits except number of supported CPUs on x86/64 (which is a
compile-time option).

Number of VCPUs per guest is limited by space in the shared_info page shared
between each guest and Xen. This limitation will go away in due course but
right now we have scalability at 4-8 VCPUs so in practise a hard limit of 16
is not the main issue.

 -- Keir

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