Re: [Xen-devel] [RFC PATCH 21/24] ARM: vITS: handle INVALL command

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Tue, 6 Dec 2016, Stefano Stabellini wrote:
> moving a vCPU with interrupts assigned to it is slower than moving a
> vCPU without interrupts assigned to it. You could say that the
> slowness is directly proportional do the number of interrupts assigned
> to the vCPU.

To be pedantic, by "assigned" I mean that a physical interrupt is routed
to a given pCPU and is set to be forwarded to a guest vCPU running on it
by the _IRQ_GUEST flag. The guest could be dom0. Upon receiving one of
these physical interrupts, a corresponding virtual interrupt (could be a
different irq) will be injected into the guest vCPU.

When the vCPU is migrated to a new pCPU, the physical interrupts that
are configured to be injected as virtual interrupts into the vCPU, are
migrated with it. The physical interrupt migration has a cost. However,
receiving physical interrupts on the wrong pCPU has an higher cost.

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