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



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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