Re: [virtio-dev] On doorbells (queue notifications)

[Alex BennÃe <alex.bennee@linaro.org>]

Stefan Hajnoczi <stefanha@redhat.com> writes:

> On Tue, Jul 14, 2020 at 10:43:36PM +0100, Alex BennÃe wrote:
>> I'm slightly confused by the MSI terminology because this only seems to
>> be relevant for the PCI legacy interface and AFAICT only touch the
>> outgoing path in setup and del_vq. Do incoming MSI interrupts just get
>> mapped directly to the appropriate handler function to process the
>> queues or the config?
>
> When MSI is used the VIRTIO ISR register does not need to be read by the
> guest interrupt handler.
>
>> Finally I'm curious if this is just a problem avoided by the s390
>> channel approach? Does the use of messages over a channel just avoid the
>> sort of bouncing back and forth that other hypervisors have to do when
>> emulating a device?
>
> What does "bouncing back and forth" mean exactly?

Context switching between guest and hypervisor.

>
> Stefan


-- 
Alex BennÃe