as was explained, the loop needs to be "for i:=0; i < b.N; i++"
as was mentioned, the compiler's dead code elimination efforts can
frustrate benchmarking. they way to make sure the test code survives is to
not let it be dead code. for example
// external var dummy
func
for i:=0; i < b.N; i++ {
dummy += rand.Int63()
}
On Tue, May 19, 2020 at 10:22 AM Warren Bare <warren.b...@gmail.com> wrote:
> >You are supposed to run the loop b.N times, not some fixed constant.
>
> I understand. This is a simulation of a single bigger task that takes a
> while. I'm not trying to time the rand function inside the loop. The loop
> is simply to burn time. This simple function is a minimal example that
> demonstrates a problem I was having with my own real benchmark test.
>
> I don't know for sure that the compiler is NOT optimizing away this rand
> function, but I can tell you this problem was happening on my own code that
> can not be optimized away.
>
> Thanks.
>
>
>
> On Tuesday, May 19, 2020 at 12:39:33 PM UTC-4, Volker Dobler wrote:
>>
>> You are supposed to run the loop b.N times, not
>> some fixed constant. Also make sure the compiler
>> doesn't optimize away the whole function.
>>
>> V.
>>
>> On Tuesday, 19 May 2020 18:20:43 UTC+2, Warren Bare wrote:
>>>
>>> Hi Folks,
>>>
>>> I'm getting weird results from Benchmark. Maybe someone can help me
>>> understand this. I'm running on amd-64 (Threadripper 16 core 32 thread)
>>> Windows 10. Go 1.14.3
>>>
>>> I have the benchmark below (main_test.go) on a minimum "hello world"
>>> main.go (just like playground).
>>>
>>> When I run the benchmark as it is below, I get the results included just
>>> below here. Notice it reports 0.135 ns/op but the time is actually 135
>>> *ms* so it is off by a factor of 1 billion. It is like it trying to
>>> report in seconds but did not change the label from ns to s.
>>>
>>> Further, if I increase the loop 10x from 10_000_000 to 100_000_000, then
>>> it prints Duration 1.349 seconds (good) and now the Benchmark time has
>>> increased by a factor of 10 *billion *and is now correctly reported as
>>> 1349224200 ns/op
>>>
>>> What am I missing here?
>>>
>>>
>>> BenchmarkMarshalSample-32 1000000000 0.135 ns/op
>>> 0 B/op 0 allocs/op
>>> --- BENCH: BenchmarkMarshalSample-32
>>> main_test.go:14: Duration 136.1221ms
>>> main_test.go:14: Duration 135.1214ms
>>> main_test.go:14: Duration 134.1763ms
>>> main_test.go:14: Duration 135.1217ms
>>> main_test.go:14: Duration 135.1298ms
>>> main_test.go:14: Duration 135.1217ms
>>> main_test.go:14: Duration 135.1218ms
>>> main_test.go:14: Duration 135.1213ms
>>> main_test.go:14: Duration 135.1298ms
>>> main_test.go:14: Duration 135.1216ms
>>> ... [output truncated]
>>> PASS
>>>
>>>
>>>
>>> package main
>>>
>>> import (
>>> "math/rand"
>>> "testing"
>>> "time"
>>> )
>>>
>>> func BenchmarkMarshalSample(b *testing.B) {
>>> start := time.Now()
>>> for i := 0; i < 10_000_000; i++ {
>>> rand.Int63()
>>> }
>>> b.Log("Duration", time.Now().Sub(start))
>>> }
>>>
>>> --
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--
*Michael T. jonesmichael.jo...@gmail.com <michael.jo...@gmail.com>*
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