How can we easily time function calls in elixir?

Question

You can write a module¹ that can measure a given function. The following function returns the runtime of a given function in seconds:

defmodule Benchmark do
  def measure(function) do
    function
    |> :timer.tc
    |> elem(0)
    |> Kernel./(1_000_000)
  end
end

Use it like this:

iex> Benchmark.measure(fn -> 123456*654321 end)
9.0e-6

If you want to use that for Benchmarking, then there is another answer.

A better approach than measuring single run execution time is to measure operations per timeframe. This takes the code under test and executes it repeatingly within a given timeframe. This methodology yields more accurate results.

There is a library called Benchwarmer you can use for that:

Add Benchwarmer to your mix.exs

def deps do
  [ { :benchwarmer, "~> 0.0.2" } ]
end

Simply pass an inline function:

iex> Benchwarmer.benchmark fn -> 123456*654321 end
*** #Function<20.90072148/0 in :erl_eval.expr/5> ***
1.2 sec     2M iterations   0.61 μs/op

[%Benchwarmer.Results{...}]

[1]: Code taken from http://www.littlelines.com/blog/2014/06/27/elixir-vs-ruby-showdown-part-one/
Benchee https://github.com/bencheeorg/benchee

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