On Wed, Oct 07, 2009 at 11:29:11AM -0400, Bill Nottingham wrote:
Richard W.M. Jones (rjones(a)redhat.com) said:
> > This is going to be pretty important for scientific workloads where
> > atlas is going to be used. I've eavesdropped on several conversations
> > where people were talking about being able to run off-the-shelf
> > science code virtual appliance in order to reduce the environment
> > configuration workload for an individual researcher.
>
> Yup. The really fun starts when you do live migration. The processor
> literally changes underneath the running programs. If you thought you
> had SSE3 one minute, then the next you don't, or vice versa.
>
> No one has to my knowledge come up with a good way to deal with this.
> But it probably involves signalling the kernel and processes so that
> they can redo processor detection. You can see why that is not going
> to be pleasant.
Surely the way to do this is to know what your workload is doing,
and not do live migration to random hardware?
Or just apply a CPUID mask to the guest, so it sees a constant set of
features no matter where its migrated to. This is what Xen, VMWare,
QEMU/KVM all do for this problem. Trying to make the guest re-detect,
while nice in theory, is just not something people are going to bother
doing - witness the death of pure paravirt, since fullyvirt is 'good
enough' for most people - the same is true of CPUID masking to make
hardware appear homogeneous
Daniel
--
|: Red Hat, Engineering, London -o-
http://people.redhat.com/berrange/ :|
|:
http://libvirt.org -o-
http://virt-manager.org -o-
http://ovirt.org :|
|:
http://autobuild.org -o-
http://search.cpan.org/~danberr/ :|
|: GnuPG: 7D3B9505 -o- F3C9 553F A1DA 4AC2 5648 23C1 B3DF F742 7D3B 9505 :|