| .. _profiling-perf: |
| |
| Perf |
| #### |
| |
| Perf is a profiler tool based on stack tracing. It can be used for lightweight profiling |
| with minimal code overhead. |
| |
| Work Principle |
| ************** |
| |
| The ``perf record`` shell command starts a timer with the perf tracer function. |
| Timers are driven by interrupts, so the perf tracer function is called during an interruption. |
| The Zephyr core saves the return address and frame pointer in the interrupt stack or ``callee_saved`` |
| structure before calling the interrupt handler. Thus, the perf trace function makes stack traces by |
| using the return address and frame pointer. |
| |
| The :zephyr_file:`scripts/profiling/stackcollapse.py` script can be used to convert return addresses |
| in the stack trace to function names using symbols from the ELF file, and to prints them in the |
| format expected by `FlameGraph`_. |
| |
| Configuration |
| ************* |
| |
| You can configure this module using the following options: |
| |
| * :kconfig:option:`CONFIG_PROFILING_PERF`: Enables the module. This option adds |
| the ``perf`` command to the shell. |
| |
| * :kconfig:option:`CONFIG_PROFILING_PERF_BUFFER_SIZE`: Sets the size of the perf buffer |
| where samples are saved before printing. |
| |
| Usage |
| ***** |
| |
| Refer to the :zephyr:code-sample:`profiling-perf` sample for an example of how to use the perf tool. |
| |
| .. _FlameGraph: https://github.com/brendangregg/FlameGraph/ |
