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

[Xen-devel] Interrupt forwarding

To: xen-devel@xxxxxxxxxxxxxxxxxxxxx
Subject: [Xen-devel] Interrupt forwarding
From: Jon Smirl <jonsmirl@xxxxxxxxx>
Date: Sat, 12 Mar 2005 13:02:37 -0500
Delivery-date: Sat, 12 Mar 2005 18:03:44 +0000
Domainkey-signature: a=rsa-sha1; q=dns; c=nofws; s=beta; d=gmail.com; h=received:message-id:date:from:reply-to:to:subject:mime-version:content-type:content-transfer-encoding; b=LOeiZjB/ToMImifK+kWxECiTZ0ZEkh1+L3fb90B7yNmhf1K2KKhhdsJKri8y0Enr7BF/sbjGh0ebMyWzSV3xm3/M/v7sNcMlniGfX4Dj6TiaPEPCMBa+hrAKFWVDZ/rzaEJdV/w0cFiIcazadMm5nI8m0AIcueYNn+Ys+8WLRWM=
Envelope-to: xen+James.Bulpin@xxxxxxxxxxxx
List-archive: <http://sourceforge.net/mailarchive/forum.php?forum=xen-devel>
List-help: <mailto:xen-devel-request@lists.sourceforge.net?subject=help>
List-id: List for Xen developers <xen-devel.lists.sourceforge.net>
List-post: <mailto:xen-devel@lists.sourceforge.net>
List-subscribe: <https://lists.sourceforge.net/lists/listinfo/xen-devel>, <mailto:xen-devel-request@lists.sourceforge.net?subject=subscribe>
List-unsubscribe: <https://lists.sourceforge.net/lists/listinfo/xen-devel>, <mailto:xen-devel-request@lists.sourceforge.net?subject=unsubscribe>
Reply-to: Jon Smirl <jonsmirl@xxxxxxxxx>
Sender: xen-devel-admin@xxxxxxxxxxxxxxxxxxxxx
The subject of interrupt forwarding just came up on lkml. How is this
dealt with in Xen? I'm not currently a Xen user so I may be
misunderstanding how it works. In Xen I believe you can assign a piece
of hardware for exclusive use from a domain. How does this work for
shared interrupts, what if the domain receiving the interrupt dies and
can't acknowledge it?

Here's my comment from lkml....

On Sat, 12 Mar 2005 10:55:21 -0500, Jon Smirl <jonsmirl@xxxxxxxxx> wrote:
> I've tried implementing this before (on UML) and could not get around the
> interrupt problem. Most interrupts on the x86 architecture are shared.
> Disabling the IRQ at the PIC blocks all of the shared IRQs. This works
> (hope your userspace handler is last on the shared handler list) until
> you have a problem in userspace.
> 
> Once you have a problem in userspace there is no way to acknowledge
> the interrupt anymore. I tried to address that by maintaining a timer
> and suspending the hardware through the D0 state to reset it. That had
> some success. Not acknowledging the interrupt results in an interrupt
> loop and reboot.
> 
> The problem can be mitigated by choosing what slot your hardware to
> put your hardware in. This can reduce the number of shared interrupts.
> If you can get exclusive use of the interrupt this method will work.
> 
> If I were designing a new bus I would make interrupt acknowledge part
> of PCI config space in order to allow a single piece of code to
> acknowledge them. Since we can't change the bus the only safe way to
> do this is to build a hardware specific driver for each device to
> acknowledge the interrupt.
> 
> Bottom line is that I could find no reliable solution for handing interrupts.


-- 
Jon Smirl
jonsmirl@xxxxxxxxx


-------------------------------------------------------
SF email is sponsored by - The IT Product Guide
Read honest & candid reviews on hundreds of IT Products from real users.
Discover which products truly live up to the hype. Start reading now.
http://ads.osdn.com/?ad_id=6595&alloc_id=14396&op=click
_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxxxx
https://lists.sourceforge.net/lists/listinfo/xen-devel