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Re: [Xen-devel] Interrupt to CPU routing in HVM domains - again

To: John Levon <levon@xxxxxxxxxxxxxxxxx>, James Harper <james.harper@xxxxxxxxxxxxxxxx>
Subject: Re: [Xen-devel] Interrupt to CPU routing in HVM domains - again
From: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
Date: Fri, 05 Sep 2008 08:44:23 +0100
Cc: xen-devel@xxxxxxxxxxxxxxxxxxx, bart brooks <bart_brooks@xxxxxxxxxxx>
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Thread-topic: [Xen-devel] Interrupt to CPU routing in HVM domains - again
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On 5/9/08 02:21, "John Levon" <levon@xxxxxxxxxxxxxxxxx> wrote:

>> Have I understood correctly that only cpu 0 of the vcpu_info[] array is
>> ever used even if the interrupt actually occurs on another vcpu? Is this
>> true for all versions of Xen? It seems that Bart's experience is exactly
>> the opposite of mine - the change that fixed up the performance issues
>> for me caused performance issues for him...
> I was just in this code. From what I can tell it's a requirement that
> all the domU's event channels be bound to VCPU0, since there's no code
> in Xen itself that will redirect evtchn_pending_sel from another VCPU to
> CPU0's vcpu_info, and the callback IRQ code assumes VCPU0.

Yes, this is very likely the problem being observed.

 -- Keir

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