export_stacks(path, metric='self_cpu_time_total')
  Save stack traces in a file in a format suitable for
  visualization.

  Parameters:
     * **path** (*str*) -- save stacks file to this location;

     * **metric** (*str*) -- metric to use: "self_cpu_time_total"
       or "self_cuda_time_total"

  Note:

    Example of using FlameGraph tool:

    * git clone https://github.com/brendangregg/FlameGraph

    * cd FlameGraph

    * ./flamegraph.pl --title "CPU time" --countname "us."
      profiler.stacks > perf_viz.svg

key_averages(group_by_input_shape=False, group_by_stack_n=0)
  Averages events, grouping them by operator name and (optionally)
  input shapes and stack.

  Note:

    To use shape/stack functionality make sure to set
    record_shapes/with_stack when creating profiler context
    manager.
