[lttng-dev] Lttng user application tracing

[Jérémie Galarneau]

On Tue, May 5, 2015 at 12:55 PM, Beatriz Aguilar <beatriz.aguilar at bsc.es>
wrote:

> Hi,
>
> I am trying to trace a user application with Lttng.
> I would like to know if it is possible to do it without introducing
> tracepoints in the user code like when the kernel is traced.
>
> For example, I would like to see what every CPU/process is doing in an MPI
> + OpenMP application without putting  tracepoints in it.
>

Hi Beatriz,

Without instrumenting your application, you will be limited to the
information provided by the kernel instrumentation which includes syscalls.
Those can already provide you with quite a bit of information to understand
what an application is doing.

Moreover, you can use a couple of lttng-ust helper libraries to trace calls
to some libc functions [1]. You could probably develop other helpers based
around the same idea (overloading symbols) to trace MPI and OpenMP calls
[2].

Unfortunately, if you really want to instrument your application's
internals, you will have to manually add tracepoints to the code. Dynamic
tracing, which we don't support yet, would let you insert probes at runtime
without the need for this static instrumentation.

Regards,
Jérémie

[1] http://lttng.org/docs/#doc-prebuilt-ust-helpers
[2] https://github.com/lttng/lttng-ust/tree/master/liblttng-ust-libc-wrapper


>
> Is that possible or is there any alternative to Lttng to generate ctf
> traces?
>
> Thank you very much.
> Your help is very much appreciated =)
>
>
> Beatriz Aguilar
>
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-- 
Jérémie Galarneau
EfficiOS Inc.
http://www.efficios.com
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