Re: [lttng-dev] LTTNG-ust detailed architecture?

[Scheler, Fabian (CT RDA IOT SES-DE)]

Hi,

thanks for your answer!

We have been using LTTng-UST for hard real-time systems for a while.
Once tracing is setup, there are few interactions between the traced
application and the rest. The tracing code simply fills the
sub-buffers and switches to another sub-buffer when the current one
is full. In one mode, the consumer daemon polls the state of tracing
sub-buffers to know when they are full and can be copied and emptied;
the traced application does not have to issue any potentially
blocking system call. In the default mode, the traced application
sends a short message on a pipe to the consumer daemon to signal when
a sub-buffer is ready to be consumed.

- What is the purpose of the shared memory in the ringbuffer (shm.{c,h})?
- How does the consumerd poll the buffers?
- ...



Ciao
Fabian

In principle, this sounds quite well, but there are still plenty of other thinks we would like to know in more detail: - How does the ust_listener_thread interact with the instrumented application? - How does the ust_listener_thread interact with the consumderd (I guess your answer targeted this part, right?) and/or the sessiond? So, it would be really great if there is some document where this architecture is noted down. Maybe, there are also helpful comments in the code - if you can point me there, this would also be helpful.

----- Le 24 Oct 18, à 6:53, Scheler, Fabian (CT RDA IOT SES-DE)
fabian.sche...@siemens.com a écrit :

Hi,

we would like to trace real-time applications and we consider
LTTNG-ust as one possible way to do this. But before we go for
LTTNG-ust, we need to estimate the impact LTTNG-ust could have on
the instrumented application. While I consider the user-manual of
LTTNG-ust to be really great, I am missing a more detailed
architecture documentation, that would be really helpful to answer
this question.

Having a look at the picture here

https://lttng.org/docs/v2.10/#doc-plumbing

I want to review these component interactions more closely:

1. Session daemon -> liblttng-ust


run-time behavior of the instrumented application, when it comes
to

- submitting events to the buffer

* Which component controls/instantiates/maintains the buffer? * How
is the buffer synchronized?

- setting event-rules (i.e. enabling/disabling events) - starting
tracing sessions - ...

* What does happen along the red dashed arrow "Session Daemon ->
liblttng-ust"?

2. liblttng-ust -> Consumer daemon

At some point the consumer daemon reads the events stored in the
buffer and writes them to some output-file.

* What does happen along the violet arrow "liblttng-ust -> Consumer
daemon"? * Could the instrumented application be affected here
somehow?

Is this documented somewhere - maybe I simply missed it.

Ciao Fabian -- With best regards, Dr. Fabian Scheler

Siemens AG Corporate Technology Research and Development for
Digitalization and Automation Smart Embedded Systems CT RDA IOT
SES-DE Guenther-Scharowsky-Str. 1 91058 Erlangen, Germany Tel.: +49

This library seems to create a new thread in the context of the instrumented application. How could this thread impact the 1522 1702973 Mobile: +49 1522 1702973 mailto:fabian.sche...@siemens.com

www.siemens.com/ingenuityforlife


and Chief Executive Officer; Roland Busch, Lisa Davis, Klaus
Helmrich, Janina Kugel, Cedrik Neike, Michael Sen, Ralf P. Thomas;
Registered offices: Berlin and Munich, Germany; Commercial
registries: Berlin Charlottenburg, HRB 12300, Munich, HRB 6684;
WEEE-Reg.-No. DE 23691322


_______________________________________________ lttng-dev mailing

Siemens Aktiengesellschaft: Chairman of the Supervisory Board: Jim Hagemann Snabe; Managing Board: Joe Kaeser, Chairman, President list lttng-dev@lists.lttng.org https://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev

--
With best regards,
Dr. Fabian Scheler

Siemens AG
Corporate Technology
Research and Development for Digitalization and Automation
Smart Embedded Systems
CT RDA IOT SES-DE
Guenther-Scharowsky-Str. 1
91058 Erlangen, Germany
Tel.: +49 1522 1702973
Mobile: +49 1522 1702973
mailto:fabian.sche...@siemens.com

www.siemens.com/ingenuityforlife

Siemens Aktiengesellschaft: Chairman of the Supervisory Board: Jim
Hagemann Snabe; Managing Board: Joe Kaeser, Chairman, President and
Chief Executive Officer; Roland Busch, Lisa Davis, Klaus Helmrich,
Janina Kugel, Cedrik Neike, Michael Sen, Ralf P. Thomas; Registered
offices: Berlin and Munich, Germany; Commercial registries: Berlin
Charlottenburg, HRB 12300, Munich, HRB 6684; WEEE-Reg.-No. DE 23691322

smime.p7s
Description: S/MIME Cryptographic Signature

_______________________________________________
lttng-dev mailing list
lttng-dev@lists.lttng.org
https://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev