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SubjectRe: PPP slowdown (Was Re: No Interrupt latency but too many interrupts)
> > I observed that my system still has a load of 0.30 when totally idle
> > so I had a look at the interrupts and although the serial port
> > was not in use there were still a couple of hundred interrupts
> > per second.
>
> I think this may be a separate problem. My loadav is usually 0.01 to 0.03
> but I still get PPP slowdown.
You are right. There was a FAX transmission that was desperately trying
to complete but had timeouts because of the serial performance.
I just checked for PPP or dialup events before I posted. Sorry.
>
> > How could the serial port generate so many interrupts while not in use?
>
> Where do you get this info ? /proc/interrupts doesn't seem to report this.
It does. Just do a repeated cat /proc/interrupts and see how the values
change.
>
> > Were there any modifications to the serial driver lately?
>
> In my searches through the kernel patches I mentioned, I have found only
> two major changes within the serial/ppp code. These are the addition of
> IPX (which I think is the likely culprit), and the addition of some
> additional ioctls. All of this is part of the 1.3.72 patch which is about
> when the complaints started (correct me if that's wrong).
There is also a major reworking of the Interrupt code in arch/i386/irq.c
which could be the culprit. Someone mentioned that the timer code also
was changed.


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