Can KVM CPU assignment count differ from physical hosts CPU count?

Posted by javano on Server Fault See other posts from Server Fault or by javano
Published on 2012-10-05T13:43:16Z Indexed on 2012/10/05 15:40 UTC
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kvm-virtualization

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scheduling

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vcpu

I have read this question. I knew already that I could for example, have a quad core machine with four guests each having two vCPUs. As they don't all be require 100% CPU usage all the time, the scheduler would handle this for me.

My question is about how this relates to a fail-over or migration situation;

If host1 has two dual-core CPUs, and I assign guest1 four vCPUs (so it accessed all four physical cores), what will happen if I try and migrate it to host2 which only has one dual-core CPU?

Can qemu-kvm emulate more vCPUs than there are physical? Or would I have to shut down the virtual machine, change the CPU assignment, migrate it, and then boot it back up (so no live migration)?

Many thanks.

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