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SubjectRe: 2.6.24 says "serial8250: too much work for irq4" a lot.

* H. Peter Anvin <hpa@zytor.com> wrote:

>> (If it's a qemu issue, I can go bother them. It's possible that qemu
>> isn't delivering interrupts as often as it expects, since that's
>> limited by the granularity of the host timer; I know the clock in
>> qemu can run a bit slow because it only gets clock interrupts when
>> the host system isn't too busy to schedule the emulator. But this
>> doesn't usually cause a problem. I _think_ the message is just a
>> "this should never happen" type warning, which is happening to me.
>> But I break stuff. :)
>
> This is because Qemu spews data to the serial port without any rate
> limiting; this causes the in-kernel serial port driver to think the
> port is stuck. The serial port emulation needs to make it possible to
> drain the virtual FIFO every now and then, as opposed to filling it
> again immediately.

actually, the way i solved it for qemu+KVM+paravirt was to just turn off
this rather silly check in the serial driver if inside a paravirt guest.
When we are emulated then the serial 'hardware' is totally reliable and
we should just trust it. That way i never dropped a single bit of kernel
log output again.

Ingo


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