Re: Hypercall continuation and wait_event

[Keir Fraser <keir.xen@gmail.com>]

It means the vcpu has an interrupt pending (in the pv case, that means an
event channel has a pending event).


On 09/04/2012 21:16, "Ruslan Nikolaev" <nruslan_devel@yahoo.com> wrote:

> Keir,
> 
> Thanks for your replies! Just one more question about
> local_event_need_delivery(). Under what (common) conditions I would expect to
> have local events that need delivery?
> 
> Ruslan
> 
> 
> 
> ----- Original Message -----
> From: Keir Fraser <keir.xen@gmail.com>
> To: Ruslan Nikolaev <nruslan_devel@yahoo.com>; "xen-devel@lists.xen.org"
> <xen-devel@lists.xen.org>
> Cc: 
> Sent: Monday, April 9, 2012 8:09 PM
> Subject: Re: [Xen-devel] Hypercall continuation and wait_event
> 
> On 09/04/2012 20:18, "Ruslan Nikolaev" <nruslan_devel@yahoo.com> wrote:
> 
>> Thanks for the reply.
>> 
>> Since it can take arbitrarily long for an event to arrive (e.g., it is coming
>> from a different guest on a user request), how do I need to handle this
>> case?Does it mean that I only need to make sure that nothings get scheduled
>> on
>> this VCPU in the guest?
> 
> Nothing else *can* get scheduled on this VCPU in the guest. The VCPU will
> sleep within wait_event within the hypercall context. Hence you must not
> hold any hypervisor spinlocks either, for example.
> 
>> Also, it is not exactly clear to me how wait_event avoids the need for
>> hypercall continuation. What about local_events_need_delivery() or
>> softirq_pending()? Are they going to be handled by wait_event internally?
> 
> Your VCPU gets descheduled. Hence softirq_pending() is not your concern for
> the duration that you're descheduled. And if local_event_need_delivery(),
> that's too bad, they have to wait for the vcpu to wake up on the event.
> 
> -- Keir
> 
>> Ruslan
>> 
>> 
>> 
>> 
>> 
>> 
>> ----- Original Message -----
>> From: Keir Fraser <keir.xen@gmail.com>
>> To: Ruslan Nikolaev <nruslan_devel@yahoo.com>; "xen-devel@lists.xen.org"
>> <xen-devel@lists.xen.org>
>> Cc: 
>> Sent: Monday, April 9, 2012 6:54 PM
>> Subject: Re: [Xen-devel] Hypercall continuation and wait_event
>> 
>> On 09/04/2012 18:51, "Ruslan Nikolaev" <nruslan_devel@yahoo.com> wrote:
>> 
>>> Hi
>>> 
>>> I am curious how I can properly support hypercall continuation and
>>> wait_event.
>>> I have a dedicated VCPU in a domain which makes a special hypercall, and the
>>> hypercall waits for certain event to arrive. I am using queues available in
>>> Xen, so wait_event will be invoked in the hypercall once its ready to accept
>>> events. However, my understanding that even though I have a dedicated VCPU
>>> for
>>> this hypercall, I still may need to support hypercall continuation properly.
>>> (Is this the case?) So, my question is how exactly the need for hypercall
>> 
>> No it's not the case, the old hypercall_create_continuation() mechanism does
>> not need to be used with wait_event().
>> 
>> -- Keir
>> 
>>> preemption may affect wait_event() and wait() operations, and where would I
>>> need to do hypercall_preempt_check()?
>>> 
>>> Thank you!
>>> Ruslan
>>> 
>>> 
>>> _______________________________________________
>>> Xen-devel mailing list
>>> Xen-devel@lists.xen.org
>>> http://lists.xen.org/xen-devel
>> 
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> 
> 
> 
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