how to fix "interrupt storm"

[perryh at pluto.rain.com]

"Paul B. Mahol" <onemda at gmail.com> wrote:
> On 5/10/09, perryh at pluto.rain.com <perryh at pluto.rain.com> wrote:
...
> >> >> >   interrupt storm detected on "irq9:"; throttling interrupt source
> >> >> >   interrupt storm detected on "irq9:"; throttling interrupt source
> >> >> >   ad6: FAILURE - SET_MULTI status=51<READY,DSC,ERROR>
> >> >> >    error=4<ABORTED>
> >> >> >   ad6: TIMEOUT - READ_DMA retrying (1 retry left) LBA=136936
> >> >> >
> >> >> > etc. etc. until I killed it with ^C ...
> >> >>
> >> >> Output of "vmstat -i"?
> >> >
> >> > $ vmstat -i
> >> > interrupt                          total       rate
> >> > irq0: clk                      497386851       1004
> >> > irq1: atkbd0                        2491          0
> >> > irq3: xl0                           2030          0
> >> > irq6: fdc0                            11          0
> >> > irq7: ppbus0 ppc0                      1          0
> >> > irq8: rtc                       63654324        128
> >> > irq9: uhci0+                      166216          0
> >>
> >> uhci0 is doing strange things, what usb device are connected?
> >
> > There are no USB devices connected.  I think those must actually
> > be atapci1 interrupts, since irq9 is where dmesg reported it.
>
> Try editing /boot/device.hints lines with irq or adding similar
> lines ...

How would I go about figuring out what to add or change?

I suppose I want to move either uhci0 or atapci1 to an unused irq,
but my recollection is that I don't have unlimited choice in the
matter because the IRQ used by a particular PCI device -- or at
least the set available for assignment -- is determined by how the
motherboard is wired.

Granted it's been several years since I was into PCI at this level.