Xen devel - Oct 2009 - At what places is an event handler called besides a hypercall?

Hi, folks. I''m puzzled when the event handler is called in xen.
I''ve only
found a pending check and an upcall at the end of each hypercall. And an
event delivery will cause a schedule, but no calling to the handler. So it
seems when a domain sends a event to the other, the handler of that domain
won''t be called until it makes a hypercall or check it itself. That
sounds
not so reasonable. Could anyone tell me the truth? Thanks!

Cheers,

Wu Shu


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On 22/10/2009 08:34, "Shu Wu" <superwushu@gmail.com> wrote:
> Hi, folks. I''m puzzled when the event handler is called in xen.
I''ve only
> found a pending check and an upcall at the end of each hypercall. And an
event
> delivery will cause a schedule, but no calling to the handler. So it seems
> when a domain sends a event to the other, the handler of that domain
won''t be
> called until it makes a hypercall or check it itself. That sounds not so
> reasonable. Could anyone tell me the truth? Thanks!
Events are checked for on any return to guest context. If the event sender
sees the receiver is running on another CPU, it sends an IPI, and on return
to guest context from that IPI the receiving CPU will deliver the event to
the receiving guest.

 -- Keir



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Yeah, I see it! Especially in the exception handler there is a call to
test_all_events, which checks the event and calls the handler. All these
will happen frequently. Thanks a lot!

2009/10/22 Keir Fraser <keir.fraser@eu.citrix.com>
> On 22/10/2009 08:34, "Shu Wu" <superwushu@gmail.com> wrote:
>
> > Hi, folks. I''m puzzled when the event handler is called in
xen. I''ve only
> > found a pending check and an upcall at the end of each hypercall. And
an
> event
> > delivery will cause a schedule, but no calling to the handler. So it
> seems
> > when a domain sends a event to the other, the handler of that domain
> won''t be
> > called until it makes a hypercall or check it itself. That sounds not
so
> > reasonable. Could anyone tell me the truth? Thanks!
>
> Events are checked for on any return to guest context. If the event sender
> sees the receiver is running on another CPU, it sends an IPI, and on return
> to guest context from that IPI the receiving CPU will deliver the event to
> the receiving guest.
>
>  -- Keir
>
>
>

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