Re: [Xen-devel] SMP guest support in unstable tree.

[Andrew Theurer <habanero@xxxxxxxxxx>]

Christian Limpach wrote:

> The unstable tree now includes support for SMP guests, i.e.
> domains which run on multiple cpus.  SMP guests can use between
> 1 and 32 virtual cpus, even if the machine has fewer physical cpus.
> The code is highly experimental and performance will improve over
> time.
>
> To use SMP guests:
> - enable option CONFIG_SMP in the Linux 2.6 kernel config
> - dom0 will boot with upto the number of physical cpus in the machine.
> - domU will boot with as many cpus as has been configured by setting
>  the XEN_VCPUS environment variable in xend's environment.
> - the number of cpus used can be reduced by using the maxcpus= option
>  on the Linux kernel command line.
>
>    christian
This is great news, and I hope to start experimenting with this asap.  I 
do have some questions:
Do you think there would be any room for "dedicated" cpus in a domain, 
like a one-to-one mapping of physical cpu to domain cpu?  I am asking 
because I think there would be situations where (a) one would want to 
discretely divide a large system, in particular one with numa 
characteristics where one could dedicate cpus and memory close to each 
other and (b) perhaps in this one to one mapping, there might be less 
overhead of managing cpus in a domain, vs (assuming) some sort of 
timesharing of a physical cpu to many domains, and even more than one 
virtual cpu in just one domain. 

Anyway, I am mostly curious at this point.  This is just what I have 
seen in the ppc/power5 world, a choice of dedicated cpus (however, if 
they are idle that cpu can be "shared" if desired) or virtual cpus (up 
to 64 I think) backed by N physical cpus.
Andrew Theurer


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