[ltt-dev] Problem with tracing network events in 0.128 to 0.132

Mathieu Desnoyers compudj at krystal.dyndns.org
Fri May 1 18:03:14 EDT 2009

* Gregory Haskins (ghaskins at novell.com) wrote:
> Hi Mathieu, ltt-devs,
>   Ive been noticing that some network related events are missing from my
> traces yet when running with 30-rc2 -0.132 (and same issue was in 0.128).
> I am running with ltt-statedump, kernel-trace, and net-trace loaded (and
> ltt-armall after the fact).  What I see is that the interrupt for my
> ethernet NIC and SOFTIRQ-3 never show up in the trace, even though they
> clearly must be getting called as I can see other activity related to
> packets being processed (such as the socket application running and
> sleeping).  This same problem has been observed on two completely
> different machines, so its not limited to a particularly funky hardware
> configuration or anything like that.  It should also be noted that this
> worked on both machines in past releases of LTT (for instance, the 29
> series).
> I am running the latest  userspace as well (ltt-control-0.67 and
> lttv-0.12.12).  This used to work, so I suspect it might be a
> regression.  Of course, operator error is always a possibility as well ;)
> I am willing to dig in and see if I can fix it, but I figured I would
> post first to see if this is a known issue, has a workaround, or perhaps
> some guiding wisdom on what to look for first.

Hi Greg,

lttng-instrumentation-irq.patch has changed a lot between 2.6.29.x and
2.6.30 lttng. I bet the problem is there.

Ah, it is :

handle_IRQ_event is not instrumented anymore because Thomas Gleixner did
not like the fact that I separated handle_IRQ_event into an instrumented
handle_IRQ_event() calling _handle_IRQ_event() (which now contained the
real implementation).

I think I should move the trace_irq_entry/trace_irq_exit events into
handle_IRQ_event(), so we catch the calls from kernel/irq/chic.c,

This should be easy enough. I'll do it soon.


> Thanks!
> -Greg

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Mathieu Desnoyers
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