Re: [question] e1000 interrupt storm happened becauseof its corresponding ioapic->irr bit always set

[Jason Wang <jasowang@redhat.com>]

On 08/25/2014 03:17 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).
>> >
> Thanks, Jason,
> I searched "e1000 autoneg" in gmane.comp.emulators.qemu, and found below patches, 
> http://thread.gmane.org/gmane.comp.emulators.qemu/143001/focus=143007
> http://thread.gmane.org/gmane.comp.emulators.qemu/284105/focus=284765
> http://thread.gmane.org/gmane.comp.emulators.qemu/186159/focus=187351
> which one tries to fix this problem, or all of them?
>
>> >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.
>> >
> Sorry, I don't understand,
> I think one interrupt should not been enabled before its handler is successfully registered, 
> is it possible that e1000 emulation inject the interrupt before the interrupt is succesfully enabled?

There's no way for qemu to know whether or not the irq handler was
registered in guest. So if qemu behaves differently with a physical
card, it may lead the interrupt to be injected into guest too early. You
can search redhat bugzilla for lots of related bugs, some even with
in-depth analysis.

Thanks
>
> Thanks,
> Zhang Haoyu
>