`b.Loop` disables inlining, specifically. I assume in your code, `WriteFrames` gets inlined when you use `for range b.N`. After inlinining `WriteFrames`, the iterator function itself also gets inlined, as it directly `range`s over it. After that inlining step, the iterator function doesn't need to be allocated. With `for b.Loop()`, `WriteFrames` itself does not get inlined, meaning the function needs to be allocated to get passed as an argument.
On Fri, 1 Aug 2025 at 22:39, Pierre Durand <pierredur...@gmail.com> wrote: > I think it's related to the fact that b.Loop() disables some > optimizations, but I'm not sure. > > Le vendredi 1 août 2025 à 22:33:56 UTC+2, Pierre Durand a écrit : > >> I can reproduce the issue with this code >> https://github.com/pierrre/go-libs/blob/31bec3f12a86382924cc0b486c2008db062a14bd/runtimeutil/runtimeutil_test.go#L101-L118 >> Sorry I can't write a smaller code snippet, because I think it's related >> to escape analysis, and I don't fully understand it. >> >> As you can see, I'm benchmarking the same function WriteFrames() with the >> old and the new benchmarking methods. >> >> When I run the benchmark, here is the result >> >> go test -v -run=^$ -bench="^BenchmarkWriteFrames" -benchmem ./runtimeutil >> goos: linux >> goarch: amd64 >> pkg: github.com/pierrre/go-libs/runtimeutil >> cpu: Intel(R) Core(TM) i7-8750H CPU @ 2.20GHz >> BenchmarkWriteFrames >> BenchmarkWriteFrames-12 366825 3091 ns/op >> 0 B/op 0 allocs/op >> BenchmarkWriteFramesNew >> BenchmarkWriteFramesNew-12 328620 3445 ns/op >> 80 B/op 4 allocs/op >> PASS >> ok github.com/pierrre/go-libs/runtimeutil 2.303s >> >> >> >> Le ven. 1 août 2025 à 22:04, Junyang Shao <shaoj...@google.com> a écrit : >> > >> > Hello Pierre, >> > >> > Thank you for bringing up this issue. >> > >> > May you share the code snippet that triggers this behavior? Thanks. >> >> > >> > On Fri, Aug 1, 2025 at 12:50 PM Pierre Durand <pierre...@gmail.com> >> wrote: >> >> >> >> Hello >> >> >> >> I noticed a weird behavior when I'm benchmarking with testing.B.Loop() >> code that uses iterators . >> >> The benchmark shows allocations where I start to iterate the iterator, >> and where I declare variables (before the loop) that are used inside the >> iterator loop. >> >> I know that my code is not doing any allocation, so it's strange. >> >> If I change my benchmark to use the old "range b.N", then it doesn't >> show this strange behavior. >> >> If I check allocations with "testing.AllocsPerRun", I don't see any >> allocation. >> >> >> >> Is that a know issue ? Should I open a bug ? >> >> What should I do ? Use the old benchmarking method ? >> >> >> >> Regards >> >> >> >> -- >> >> You received this message because you are subscribed to the Google >> Groups "golang-nuts" group. >> >> To unsubscribe from this group and stop receiving emails from it, send >> an email to golang-nuts...@googlegroups.com. >> >> To view this discussion visit >> https://groups.google.com/d/msgid/golang-nuts/70456dc1-3380-40fd-951d-e52275bc48a5n%40googlegroups.com >> . >> > >> > >> > >> > -- >> > Thanks, >> > Junyang >> >> >> >> -- >> Pierre Durand >> > -- > You received this message because you are subscribed to the Google Groups > "golang-nuts" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to golang-nuts+unsubscr...@googlegroups.com. > To view this discussion visit > https://groups.google.com/d/msgid/golang-nuts/f7519a16-a4cd-4d98-8559-bc1cfe5c8fdfn%40googlegroups.com > <https://groups.google.com/d/msgid/golang-nuts/f7519a16-a4cd-4d98-8559-bc1cfe5c8fdfn%40googlegroups.com?utm_medium=email&utm_source=footer> > . > -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. To view this discussion visit https://groups.google.com/d/msgid/golang-nuts/CAEkBMfGa8nU4nGXa%2BLzgVa7T-dvEkjbS9LrpuSnWFJ6EhDHZdg%40mail.gmail.com.
