wiki:Developer/Tracing

Version 1 (modified by Chris Johns, on Mar 15, 2015 at 12:42:59 AM) (diff)

Top level Trace page.

Tracing

Table of Contents

  1. Tracing

RTEMS Tracing support is an on target software based system that allows users and developers see what is happening in applications, 3rd party package or the RTEMS kernel itself in real-time.

Tracing a real-time system using just software is a complex process that involves a number of components on the host and in the target working together. Software based tracing is useful because it is portable across all architectures and board support packages how-ever tracing requires instrumenting the code, which means it is altered with the addition of code to log various events and records in real-time, and there is an execution overhead which changes the real-time profile of a system. If a user is mindful of these factors and understands the nature of the trace process these effects can be compensated for.

Trace analysis of a system can help a user find complex threading, deadlock or other related real-time issues that arise in RTEMS applications. Trace analysis can also be used by a user to audit the performance or compliance of an application to verify is it performing the desired functions.

RTEMS Trace is under development and in an open project. The RTEMS Project welcome support by users providing patches or via paid support channels that allow the work to be completed.

RTEMS Trace Components:

  1. RTEMS Trace Linker
  2. Capture Engine
  3. Common Trace Format Integration
  4. Visualisation

The RTEMS Trace Linker takes the ELF files and libraries used to build a executable and performs a link that instruments the code so the functions a user is interested in generate suitable trace records. The user provides a configuration file that defines the trace set up. The instrumented code logs the trace data using the Capture Engine. This is a thread and SMP safe module of software that takes trace records and filters the data in real-time based on trace enable records and triggers. A triggered system will log into buffers trace records that are enabled. The Capture Engine maintains a trace buffer per CPU so avoid locking overheads in SMP applications.

The Capture Engine trace buffers are transferred to the host and feed into the Babletrace tool with a suitable configuration generated by the RTEMS Trace Linker to generate CTF files. The CTF files can be viewed using tools such as Trace Compass. The RTEMS Trace Linker instruments the code with the event Ids that match the CTF configuration file so Babletrace can associate the records with the specific events.

The RTEMS Trace Linker can be configured to generate other trace output and can be used to generate custom logs for any specific purpose. For example you could create a trace log that is just an Id and timestamp so you can get a profile of the performance of you code.

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