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Re: [Xen-devel] Interrupt issue for nic cards

To: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Subject: Re: [Xen-devel] Interrupt issue for nic cards
From: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
Date: Fri, 13 May 2011 14:49:15 +0100
Cc: "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, Stefano Stabellini <Stefano.Stabellini@xxxxxxxxxxxxx>, Wei Liu <liuw@xxxxxxxxx>
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On Fri, 13 May 2011, Konrad Rzeszutek Wilk wrote:
> On Fri, May 13, 2011 at 11:14:47AM +0800, Wei Liu wrote:
> > Hi, all.
> > 
> > I'm running the latest Xen unstable with Debian Squeeze as DomU in HVM mode.
> > 
> > I configured two nics:
> > 
> > vif = ['bridge=br0,model=virtio', 'type=ioemu,bridge=br0,model=rtl8139']
> > 
> > These two cards can be successfully configured in DomU. But they fail
> > to communicate with host bridge.
> > 
> > I can see packets coming out their taps, but no packets are going back
> > into DomU.
> > 
> > Stefano suggest I look into /proc/interrupts. It shows:
> > 
> > 11      0    IO-APIC-fasteoi   eth0
> > 48      0    PCI-MSI-edge   virtio0-config
> > 49      0    PCI-MSI-edge   virtio0-input
> > 50      0    PCI-MSI-edge   virtio0-output
> > 
> > It seems that there are no interrupts for those nic devices. I'm
> > pretty sure that QEMU has pushed the data back and set interrupts
> > (through msix_notify / qemu_set_irq).
> > 
> > Has anyone encountered this problem before?
> I haven't. But it looks like the NIC isn't beeing interrupted - which
> implies that QEMU hasn't sent the IRQ to the DomU to tell it: 'hey
> you got data'. It might be worth looking in QEMU and see under which
> circumstances it sends interrupts. And whether the mechanism for sending
> interrupts is KVM specific instead of being more generic (or able to
> use the Xen mechanism).

Indeed. If I am not mistaked the function that should be called within
qemu to actually inject the interrupt is xen_piix3_set_irq and should be
called bt qemu_set_irq.

It is also worth making sure you are using the very last Xen from
xen-unstable, with the two patches I sent to the list in the last two
days (they fix interrupt injection issues to HVM domains):


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