unfair VCPU scheduling: slow HVM guest boot

[Christoph Egger <Christoph.Egger@amd.com>]

Hi,

Launch a HVM guest with twice as many VCPUs as physical CPUs are in the
machine. You will notice the guest boots slow.

With xentop you see, the first VCPU is rarely scheduled once the other
VCPUs are up in the guest.
If the boot process is just waiting for the first VCPU to finish something
(e.g. handling an interrupt), then the whole boot process "freezes" until the 
first VCPU gets scheduled.

Here is an xentop line showing how unfair the VCPUs are scheduled:

VCPUs(sec):   0:         44s  1:         94s  2:         96s  3:        140s


Christoph


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