Profile your golang benchmark with pprof

The tooling in golang is a huge benefit of the language, and we can do the profiling with pprof of a benchmark in go.

We will for that take the example of Dave Cheney :

package bench
import "testing"
func Fib(n int) int {
    if n < 2 {
      return n
    }
    return Fib(n-1) + Fib(n-2)
}
func BenchmarkFib10(b *testing.B) {
    // run the Fib function b.N times
    for n := 0; n < b.N; n++ {
      Fib(10)
    }
}

on our terminal :

go test -bench=. -benchmem -cpuprofile profile.out

We can also check for the memprofile :

go test -bench=. -benchmem -memprofile memprofile.out -cpuprofile profile.out

And then we can use pprof as we are used to do :

go tool pprof profile.out
File: bench.test
Type: cpu
Time: Apr 5, 2018 at 4:27pm (EDT)
Duration: 2s, Total samples = 1.85s (92.40%)
Entering interactive mode (type "help" for commands, "o" for options)
(pprof) top
Showing nodes accounting for 1.85s, 100% of 1.85s total
      flat  flat%   sum%        cum   cum%
     1.85s   100%   100%      1.85s   100%  bench.Fib
         0     0%   100%      1.85s   100%  bench.BenchmarkFib10
         0     0%   100%      1.85s   100%  testing.(*B).launch
         0     0%   100%      1.85s   100%  testing.(*B).runN

(on this example I used the cpu file, but you can also do the same with the memory file)

Then you can also with the list command check wat in the function takes time

(pprof) list Fib
     1.84s      2.75s (flat, cum) 148.65% of Total
         .          .      1:package bench
         .          .      2:
         .          .      3:import "testing"
         .          .      4:
     530ms      530ms      5:func Fib(n int) int {
     260ms      260ms      6:   if n < 2 {
     130ms      130ms      7:           return n
         .          .      8:   }
     920ms      1.83s      9:   return Fib(n-1) + Fib(n-2)
         .          .     10:}

or event generate a graph with the web command (or png, pdf, … it also works):

(pprof) web

PS:

if you want to run only benchmark and not all the tests of your program you can also do the following command

go test -bench=. -run=^$ . -cpuprofile profile.out

using -run=^$ means =>run all test method that the name follow the following regexp, but ^$ select no test. So it only run benchmark ;)