Let me quickly point out that your logic is inverted in the second code
snippet because you break on the condition. That is most likely the
reason for the difference. I guess the second example exits on the first
iteration.
for pos := 0; true; pos++ {
if pos < suffixLen && pos < previousSuffixLen {
continue
}
break
}
On 22.06.20 14:15, Yonatan Ben-Nes wrote:
Hi,
I'm encountering a weird issue which I fail to explain. It boils down to
2 almost identical functions which give wildly different benchmark results.
The difference between the functions is that at the slow func there is a
for loop like this:
for pos := 0; pos < suffixLen && pos < previousSuffixLen; pos++ {
}
While at the fast func the loop is like this:
for pos := 0; true; pos++ {
if pos < suffixLen && pos < previousSuffixLen {
break
}
}
* do note that the check at both versions is the same.
Other than that the functions are identical but when I benchmark them I get:
$ go test -bench=Weird .
goos: linux
goarch: amd64
BenchmarkWeirdFast-4 280394 3602 ns/op
BenchmarkWeirdSlow-4 1866 618953 ns/op
It's extra weird since getting the condition check into the loop should
be the slower form, or at least that what I intuitively thought.
Also, the extra time cost is divided between the loop section and an
append function call which run immediately at the start of the function
and is not connected in any way to the for loop.
And it's extra weird as the append cost also get smaller if instead of
reading the test text from a file I just declare a string variable with
the same text for the benchmark (mind you that I b.ResetTimer() after
doing either of those options).
I attached the files to this message as they will make everything more
clear and I also added comments describing what happen at the right points.
I'm using Ubuntu 18.04 and go is version 1.14.2, and I also checked it
on a GCP compute engine and got the same results.
Any thoughts will be much appreciated as I'm totally confused here! :)
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