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RE: [Xen-devel] [VTD][patch 0/5] HVM device assignment using vt-d

  • To: "Keir Fraser" <keir@xxxxxxxxxxxxx>, "Guy Zana" <guy@xxxxxxxxxxxx>, "Kay, Allen M" <allen.m.kay@xxxxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxx>
  • From: "Tian, Kevin" <kevin.tian@xxxxxxxxx>
  • Date: Thu, 31 May 2007 23:51:27 +0800
  • Delivery-date: Thu, 31 May 2007 08:49:43 -0700
  • List-id: Xen developer discussion <xen-devel.lists.xensource.com>
  • Thread-topic: [Xen-devel] [VTD][patch 0/5] HVM device assignment using vt-d

>From: Keir Fraser [mailto:keir@xxxxxxxxxxxxx]
>Sent: 2007年5月31日 23:40
>On 31/5/07 16:30, "Tian, Kevin" <kevin.tian@xxxxxxxxx> wrote:
>> OK, my rough thought is as below:
>> The reason to change polarity, IMO, is to capture the de-assert
>> edge in the physical wire and then reflect de-assertion into the virtual
>> wire. Then allow the statistics on gsi_assert_count to be updated
>> correctly, when shared with virtual devices in Qemu.
>> My proposal is to take virtual EOI as the de-assertion hint, without
>> any change on physical RTE property like polarity. For example, the
>> flow could be following by keeping a saying hw_assert_status array for
>> all virtual GSIs: (take vioapic for example)
>Ah, okay, so no polarity switching at all. Basically use VIOAPIC EOI as a
>hint to tentatively drop the virtual wire to LOW, and only then ->end the
>physical interrupt. I guess this is pretty much what you already
>in your VT-d patches?
>It'd be interesting to know how these two approaches compare
>performance-wise. I suppose yours should win, really, due to fewer
>If this is how your current VT-d patches handle interrupts then I don't see
>why ioapic_ack=new is not working for you. That's a bit weird. I guess I
>could read the patches some more. ;-)
> -- Keir

Oh, I'm not the author of VT-d patches which is the credit of Allen and
Xiaohui. :-) I just had the concrete thought along with the discussion 
with you, and will talk to them for confirmation tomorrow. I guess 
"ioapic_ack=new" should be just some manual bug since one NIC 
assignment shouldn't result shared interrupt case yet.


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