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[Xen-devel] Question about evtchn_callback reentry

To: "Keir Fraser" <Keir.Fraser@xxxxxxxxxxxx>
Subject: [Xen-devel] Question about evtchn_callback reentry
From: "Xu, Anthony" <anthony.xu@xxxxxxxxx>
Date: Mon, 18 Dec 2006 13:28:08 +0800
Cc: xen-devel@xxxxxxxxxxxxxxxxxxx, xen-ia64-devel <xen-ia64-devel@xxxxxxxxxxxxxxxxxxx>
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Thread-topic: [Xen-devel] Question about evtchn_callback reentry
Hi Keir,

I have some questions about evtchn_callback,

As we know all external interrupts and events are deliver to dom0 by
evtchn_callback,

Are evtchn_callback reentered?

I mean when evtchn_callbacak is executing on dom0,

Another external interrupt or event may happen, can this event be
deliverred immediately?

I found __sti will set vcpu_info-> evtchn_upcall_mask=0, which permits
event deliverring.

and __sti may be called at any device driver. 

If evtchn_callback can be reentered, how does it hanlde external
interrupt privilege?

If there is no special handling, low privileged interrupt may
"interrupt" high privileged interrupt.


BTW,
I do see evtchn_callback reentry happen on IPF dom0, and that incur
about 5% performance degradation
with KB on VTI-domain compared to non_reentry.



Thanks,
Anthony

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