[lttng-dev] lost trace events

[Alok Priyadarshi]

Awesome, I tried the intersect_mode parameter and it worked. No more lost
events. Thanks for your support.

On Thu, Nov 8, 2018 at 3:44 PM Jérémie Galarneau <
jeremie.galarneau at efficios.com> wrote:

> On Thu, 8 Nov 2018 at 18:31, Alok Priyadarshi <alokpr at gmail.com> wrote:
> >
> > Jonathan: The system is x86_64, 16 cores, no cpu affinity set. Not too
> sure about load yet.
> >
> > Mathieu: The explanation makes sense. Running babeltrace with
> --stream-intersection flag did filter out a lot of events. However it is
> hard to verify the filtered result because we do not yet know how to read
> the text format. Does the babeltrace python API support stream intersection
> by any chance?
>
> Hi Alok,
>
> The TraceCollection constructor accepts an "intersect_mode" parameter
> which will provide the same semantics as --stream-intersection.
>
> Regards,
> Jérémie
>
> >
> >
> > On Thu, Nov 8, 2018 at 9:52 AM Mathieu Desnoyers <
> mathieu.desnoyers at efficios.com> wrote:
> >>
> >> Hi Alok,
> >>
> >> With a snapshot trace, you can end up with some per-cpu buffers that
> contain information
> >> going further back in time compared to other per-cpu buffers. This
> depends on the level of
> >> system activity and tracing throughput for each CPU.
> >>
> >> The situation you experience can very well be triggered by having the
> begin event on one CPU,
> >> being migrated to another CPU, and having the end event on another CPU.
> If either the
> >> source or destination CPU has been more active than the other, you may
> find that you
> >> have only the begin or the end event in your trace.
> >>
> >> This is why we implemented the "stream intersection" mode in
> babeltrace. It ensures that
> >> babeltrace cuts away trace data belonging to time spans that only
> appear in some of
> >> the streams. It is not however activated by default.
> >>
> >> To try it out, you can do this:
> >>
> >> babeltrace --stream-intersection path/to/trace
> >>
> >> Does it help ?
> >>
> >> Thanks,
> >>
> >> Mathieu
> >>
> >> ----- On Nov 7, 2018, at 7:12 PM, Alok Priyadarshi <alokpr at gmail.com>
> wrote:
> >>
> >> A custom trace event class emits "begin" and "end" events in its
> constructor and destructor respectively. So I do not think this is due to
> conditional path.
> >>
> >> Sequence of commands to capture a snapshot are:
> >> lttng create --snapshot
> >> lttng enable-event --userspace --all
> >> lttng add-context --userspace -t vpid -t vtid
> >> lttng start
> >> lttng stop
> >> lttng snapshot record
> >>
> >> We create a new session for each snapshot to make sure that the buffer
> does not have any left-over events from the previous session. But I am
> curious if lttng shares buffers between sessions or re-uses buffers from an
> old session without flushing?
> >>
> >> Note that I am using the default LTTNG_BUFFER_PER_UID mode. All
> processes for our application run under one UID, and only one tracing
> session is active at a time.
> >>
> >> On Wed, Nov 7, 2018 at 12:09 PM Jonathan Rajotte-Julien <
> jonathan.rajotte-julien at efficios.com> wrote:
> >>>
> >>> Hi Alok,
> >>>
> >>> On Wed, Nov 07, 2018 at 11:53:25AM -0800, Alok Priyadarshi wrote:
> >>> > Hi Jonathan,
> >>> >
> >>> > Thanks for your response.
> >>> >
> >>> > We are tracing function scopes. Each scope emits two events - begin
> and
> >>> > end. We noticed that some begin events did not have corresponding end
> >>> > events in the trace.
> >>>
> >>> Seems like a solid ground as long as the corresponding ending event is
> not
> >>> inside any conditional paths. I'm sure you already validated that but
> we never
> >>> know.
> >>>
> >>> >
> >>> > I have the trace with this problem available. Would that provide any
> clue?
> >>>
> >>> It could help but I presume it might contains confidential or sensible
> >>> information. Let's define the scenario first and we will go back to
> actual
> >>> trace data if needed.
> >>>
> >>> > If not, I will try to extract a small reproducer.
> >>>
> >>> That would be best. In the meantime, could you provide the exact lttng
> commands
> >>> used to setup everything and describe subsequent lttng commands used
> for
> >>> snapshot etc.
> >>>
> >>> You can omit event name or replace them with dummy name if necessary.
> >>>
> >>> Cheers
> >>>
> >>> --
> >>> Jonathan Rajotte-Julien
> >>> EfficiOS
> >>
> >>
> >> _______________________________________________
> >> lttng-dev mailing list
> >> lttng-dev at lists.lttng.org
> >> https://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev
> >>
> >>
> >> --
> >> Mathieu Desnoyers
> >> EfficiOS Inc.
> >> http://www.efficios.com
> >
> > _______________________________________________
> > lttng-dev mailing list
> > lttng-dev at lists.lttng.org
> > https://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev
>
>
>
> --
> Jérémie Galarneau
> EfficiOS Inc.
> http://www.efficios.com
>
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