Debugging Linux Kernel using ftrace Part3 - Function Graph

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Information provided by "function" tracer is a bit hard to follow. "function_graph" is another which

  • tracks the entry of the function
  • tracks the exit of the function
  • Execution Time
  • CPU on which it is running
With "function graph" tracer, you can easily follow the flow of execution within the kernel

To use function graph, $ echo function_graph > current_tracer and then cat the trace file.



  • Start of the function is denoted with '{' and end of the function is denoted with '}'. 
  • Functions that do not call any other functions, simply end with ';', also called as leaf functions
  • Duration column reports the time spent in the corresponding function. These numbers are only for the leaf functions, and the '}' symbol.
  • When the duration is greater than 10 microseconds, a '+' is shown in the DURATION column
  • When the duration is greater than 100 microseconds, a '-' is shown in DURATION column
  • When the duration is greater than 1000 microseconds, a '#' is shown in DURATION column
  • When the duration is greater than 10 milliseconds, a '*' is shown in DURATION column
  • When the duration is greater than 100 milliseconds, a '@' is shown in DURATION column
  • When the duration is greater than 1 seconds, a '$' is shown in DURATION column

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