RE: [Xen-devel] [patch] make hypercall_preempt_check() a littlemoresensitive

["Tian, Kevin" <kevin.tian@xxxxxxxxx>]

>From: Tian,Kevin
>Sent: 2006年3月31日 10:33
>>
>>This is an interesting example,  but why deliver an upcall thru the
>>HV in the first place, why not just call the evtchn handler directly?
>
>Then you may fall into dead loop, since evtchn_device_upcall tries to get
>spinlock while unmask_evtchn path may already holds the lock.
>

A more natural way to think about this model is described in the comment, 
where says to emulate hw_resend_irq behavior. On native system, such 
irq is resent to the system bus for interrupt logic to arbitrate upon priority 
and mask status. Here event is resent to let virtual interrupt logic (event 
dispatcher) to arbitrate. Such logic is (shouldn't be) unknown at the point 
of evtchn_unmask. :-)

Thanks,
Kevin

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