[lttng-dev] Trace Compass in live session

BADEUIL Thierry thierry.badeuil at thalesgroup.com
Wed Jun 13 03:48:44 EDT 2018


The end of the goal is to debug and understand how 3 applications worked together on my embedded processor. That is why I am using sched_switch option of LTTng. I can be reproduced easily. I need to work in live session because I do not have enough memory for the LTTng traces and I should need a lot of memory.

Answers inline your email with [TB1].

T : +33 1 46 133 591
(  : +33 6 85 51 28 16
  : thierry.badeuil at thalesgroup.com

-----Message d'origine-----
De : Jonathan Rajotte-Julien [mailto:jonathan.rajotte-julien at efficios.com] 
Envoyé : mardi 12 juin 2018 19:04
À : BADEUIL Thierry
Cc : lttng-dev
Objet : Re: [lttng-dev] Trace Compass in live session

Hi Thierry,

Glad you got the base setup working.

Please reply to the other thread indicating what was necessary to make it work on your end. This might be useful for other people in the future.

Now my question is what is the end goal of using the live streaming mode. Is it really necessary?
What are you trying to achieve overall? 
Are you trying to debug a certain scenario on you platform that can be reproduced easily?
Are you simply checking out how LTTng works?

Please provide more context so we can help you.

See more inline.

----- Original Message -----
> From: "BADEUIL Thierry" <thierry.badeuil at thalesgroup.com>
> To: "lttng-dev" <lttng-dev at lists.lttng.org>
> Sent: Tuesday, June 12, 2018 12:29:22 PM
> Subject: [lttng-dev] Trace Compass in live session

> Dear all,
> I have difficulties to use Babeltrace in live session and I would like to
> use Trace Compass.

What problem are you hitting?

TraceCompass does not support the live protocol. See [1] [2] for why.

[1] https://bugs.eclipse.org/bugs/show_bug.cgi?id=486728
[2] https://git.eclipse.org/r/#/c/69285/

[TB1] : Yes I know that but when the trace files are updated, TraceCompass did not upated it even with F5. I do not understand why !

> My target activated LTTng with :
> -          Lttng create test –live –set-url:’net://’

This should be: lttng create test --set-url="net://" --live

[TB1] : both solution worked on my target. Is there any difference between the two syntaxes ?

> -          Lttng enable-event sched_switch
> -          Lttng start
> My host (@ activated LTTng with :
> -          Lttng-relayd –vv

Since this seems to be working you can drop the verbose options (-vvv).

[TB1] : OK !

> Everything seems to be OK because my host received bytes from my target
> during 1 minute.

Does the event timestamps show a 1 minute difference on the console? Note that even if you see events outputted to the console during 
1 minute does not necessarily means that a full minute of "events" is present since there might be latency between a "lttng stop" and a 
complete live reception. It take more time to serialize (in time) events than to produce them.

[TB1] : If I set 1 minute of timestamp, I can watch only 1 minute of events on TraceCompass. I have got the same problem even I stopped or not lttng-relayd. If I set 2 minutes, I can watch 2 minutes etc...
> I would like to see the traces in ~/lttng-traces with TraceCompass and I can
> only watch the first second of my recording. It is impossible to see after
> (I did a lot of refresh…).

Is your session stopped/destroyed?

[TB1] : same probleme with lttng-relayd stopped or not. Remember that TraceCompass is on a host and lttng session is on my target. The connection between is via Ethernet.

If it is the case, you should be able to read the complete trace from TraceCompass or LTTng Scope. Could you upload the trace (make sure there is no private data)?

[TB1] : I can not and I do not understand why................ I did a chmod 777 on the traces and nothing changed.

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