[lttng-dev] [lttng-ust] Missing events when just before a process exits

Jonathan Rajotte-Julien jonathan.rajotte-julien at efficios.com
Tue Mar 13 11:35:04 EDT 2018

Hi Rolf,

On Tue, Mar 13, 2018 at 10:48:17AM +0000, THEUNISSEN Rolf wrote:
> Hi,
> I am currently tracing many processes with LTTng-UST on a system under heavy load, with 2 CPUs.
> The traces seem to be missing ust-events near the end of a trace. After doing some analysis, it seems that events are missing from the other CPU then the process exits on. More concretely:
> During the lifetime of a process:
> - Process X executes on CPU 0,1: all events are in the trace
> Just before the process is about to exit:
> - Process X executes on CPU 0: missing events from the trace

How are you validating this?

> A few mili-seconds later:
> - Process X executes on CPU1 and exits: The last events are in the trace

This is not expected. Do you have a reproducer so we can check what might be

We will need the version for lttng-ust, lttng-tools, babeltrace.

Note that you can run your application with lttng-ust in debug mode using
LTTNG_UST_DEBUG=y. Debug statements will be outputted on stderr.

    $ LTTNG_UST_DEBUG=y ./my_sample_app


Jonathan Rajotte-Julien

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