WARNING - OLD ARCHIVES

This is an archived copy of the Xen.org mailing list, which we have preserved to ensure that existing links to archives are not broken. The live archive, which contains the latest emails, can be found at http://lists.xen.org/
   
 
 
Xen 
 
Home Products Support Community News
 
   
 

xen-devel

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

To: "Kay, Allen M" <allen.m.kay@xxxxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: Re: [Xen-devel] [VTD][patch 0/5] HVM device assignment using vt-d
From: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>
Date: Wed, 30 May 2007 20:55:57 +0100
Delivery-date: Wed, 30 May 2007 12:52:00 -0700
Envelope-to: www-data@xxxxxxxxxxxxxxxxxx
In-reply-to: <255498EAB77FB240B3951466AD2340D502FD388A@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>
List-help: <mailto:xen-devel-request@lists.xensource.com?subject=help>
List-id: Xen developer discussion <xen-devel.lists.xensource.com>
List-post: <mailto:xen-devel@lists.xensource.com>
List-subscribe: <http://lists.xensource.com/cgi-bin/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=subscribe>
List-unsubscribe: <http://lists.xensource.com/cgi-bin/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=unsubscribe>
Sender: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
Thread-index: Acei7YJ0pr6pL1ntT2Wzdmq3YT+WeAABwdLM
Thread-topic: [Xen-devel] [VTD][patch 0/5] HVM device assignment using vt-d
User-agent: Microsoft-Entourage/11.3.3.061214
On 30/5/07 20:05, "Kay, Allen M" <allen.m.kay@xxxxxxxxx> wrote:

>     - grub.conf: use "ioapic_ack=old" for /boot/xen.gz
>       (io_apic.c contains code for avoiding global interrupt problem)

How does this new scheme work? Can it supplant the ioapic_ack=new method?
Clearly requiring the use of a hacky command-line option to make use of a
new core feature is not very nice to say the least.

It looks like the interrupt gets EOIed by writing to the IOSAPIC EOI
register. I thought that x86 IOAPICs don't have that register?

>   - Revert back to ioapic_ack=old to allow for IRQ sharing amongst
> guests.

I would expect it to work (by design at least) even with ioapic_ack=new.

Actually I also know there are some other patches coming down the pipeline
to do pci passthrough to HVM guests without need for hardware support (of
course it is not so general; in particular it will only work for one special
hvm guest). However, they deal with this interrupt issue quite cunningly, by
inverting the interrupt polarity so that they get interrupts on both +ve and
-ve edges of the INTx line. This allows the virtual interrupt wire to be
'wiggled' precisely according to the behaviour of the physical interrupt
wire. Which is rather nice, although of course it does double the interrupt
rate, which is not so great but perhaps acceptable for the kind of low
interrupt rate devices that most people would want to hand off to a hvm
guest.

 -- Keir



_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel