julia

How to obtain the execution time of a function in Julia?


I want to obtain the execution time of a function in Julia. Here is a minimum working example:

function raise_to(n)
    for i in 1:n
        y = (1/7)^n
    end
end

How to obtain the time it took to execute raise_to(10) ?


Solution

  • The recommended way to benchmark a function is to use BenchmarkTools:

    julia> function raise_to(n)
               y = (1/7)^n
           end
    raise_to (generic function with 1 method)
    
    julia> using BenchmarkTools
    
    julia> @btime raise_to(10)
      1.815 ns (0 allocations: 0 bytes)
    

    Note that repeating the computation numerous times (like you did in your example) is a good idea to get more accurate measurements. But BenchmarTools does it for you.

    Also note that BenchmarkTools avoids many pitfalls of merely using @time. Most notably with @time, you're likely to measure compilation time in addition to run time. This is why the first invocation of @time often displays larger times/allocations:

    # First invocation: the method gets compiled
    # Large resource consumption
    julia> @time raise_to(10)
      0.007901 seconds (7.70 k allocations: 475.745 KiB)
    3.5401331746414338e-9
    
    # Subsequent invocations: stable and low timings
    julia> @time raise_to(10)
      0.000003 seconds (5 allocations: 176 bytes)
    3.5401331746414338e-9
    
    julia> @time raise_to(10)
      0.000002 seconds (5 allocations: 176 bytes)
    3.5401331746414338e-9
    
    julia> @time raise_to(10)
      0.000001 seconds (5 allocations: 176 bytes)
    3.5401331746414338e-9