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Re: [Xen-devel] [PATCH v3] xen: introduce VCPUOP_register_runstate_phys_memory_area hypercall





On 11/06/2019 13:26, Andrii Anisov wrote:


On 11.06.19 15:12, Julien Grall wrote:
Julien, I'm not sure I understand how work on (p?)CPU could be delayed. We are here with interrupts enabled, so here guest would just spend his own vcpu time budget.

Xen only supports only voluntary preemption.

Oh, really? Let me look into it a bit closer.

Did you expect Xen to be fully preemptible?

The function to do the scheduling is schedule(). This is either call from a softirq or directly in a few places (e.g wait()).

The only place in this path where do_softirq() will be called is on return to the guest (see leave_hypervisor_tail).

Cheers,

--
Julien Grall

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