Benchee profile after showcase

benchmark.exs

list = Enum.to_list(1..10_000)
map_fun = fn i -> [i, i * i] end

Benchee.run(
  %{
    "flat_map" => fn -> Enum.flat_map(list, map_fun) end,
    "map.flatten" => fn -> list |> Enum.map(map_fun) |> List.flatten() end
  },
  profile_after: true
)

output

Operating System: Linux
CPU Information: AMD Ryzen 9 5900X 12-Core Processor
Number of Available Cores: 24
Available memory: 31.27 GB
Elixir 1.13.3
Erlang 24.2.1

Benchmark suite executing with the following configuration:
warmup: 2 s
time: 5 s
memory time: 0 ns
reduction time: 0 ns
parallel: 1
inputs: none specified
Estimated total run time: 14 s

Benchmarking flat_map ...
Benchmarking map.flatten ...

Name                  ips        average  deviation         median         99th %
flat_map           3.51 K      284.55 μs    ±13.79%      277.29 μs      557.14 μs
map.flatten        2.09 K      477.46 μs    ±30.97%      410.71 μs      871.02 μs

Comparison: 
flat_map           3.51 K
map.flatten        2.09 K - 1.68x slower +192.91 μs

Profiling flat_map with eprof...

Profile results of #PID<0.237.0>
#                                               CALLS     % TIME µS/CALL
Total                                           30004 100.0 6864    0.23
Enum.flat_map/2                                     1  0.00    0    0.00
anonymous fn/2 in :elixir_compiler_1.__FILE__/1     1  0.00    0    0.00
:erlang.apply/2                                     1  0.03    2    2.00
:erlang.++/2                                    10000 17.35 1191    0.12
anonymous fn/1 in :elixir_compiler_1.__FILE__/1 10000 30.29 2079    0.21
Enum.flat_map_list/2                            10001 52.33 3592    0.36

Profile done over 6 matching functions

Profiling map.flatten with eprof...

Profile results of #PID<0.239.0>
#                                               CALLS     % TIME µS/CALL
Total                                           60007 100.0 9204    0.15
Enum.map/2                                          1  0.00    0    0.00
:lists.flatten/1                                    1  0.00    0    0.00
anonymous fn/2 in :elixir_compiler_1.__FILE__/1     1  0.01    1    1.00
List.flatten/1                                      1  0.01    1    1.00
:erlang.apply/2                                     1  0.02    2    2.00
anonymous fn/1 in :elixir_compiler_1.__FILE__/1 10000 16.17 1488    0.15
Enum."-map/2-lists^map/1-0-"/2                  10001 26.81 2468    0.25
:lists.do_flatten/2                             40001 56.98 5244    0.13

Profile done over 8 matching functions