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-ustThis library seems to create a new thread in the context of the instrumented application. How could this thread impact the 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
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Smart Embedded Systems
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