Re: [Qemu-devel] [question] e1000 interrupt storm happened because of its corresponding ioapic->irr bit always set

[Jason Wang]

On 08/23/2014 06:36 PM, Zhang Haoyu wrote:
> Hi, all
>
> I use a qemu-1.4.1/qemu-2.0.0 to run win7 guest, and encounter e1000 NIC 
> interrupt storm, 
> because "if (!ent->fields.mask && (ioapic->irr & (1 << i)))" is always true 
> in __kvm_ioapic_update_eoi().
>
> Any ideas?

We meet this several times: search the autoneg patches for an example of
workaround for this in qemu, and patch kvm: ioapic: conditionally delay
irq delivery during eoi broadcast for an workaround in kvm (rejected).

That was probably caused by something wrong in e1000 emulation which
causes interrupt to be injected into windows guest before its interrupt
handler is registered. And Windows guest does not have a mechanism to
detect and disable irq in such condition.

e1000 emulation is far from stable and complete (e.g run e1000 ethtool
selftest in linux guest may see lots of errors). It's complicate and
subtle (even has undocumented registers and behaviour). You should
better consider to use virtio which are more stable and fast in a kvm
guest (unless some intel guys are involved to improve e1000 emulation).

Thanks
>
> Thanks,
> Zhang Haoyu
>
>