On Thursday, December 15, 2016 at 6:50:14 AM UTC+8, not...@google.com wrote: > > Be wary of slice size, as caching is going to have an extremely strong > effect on the results. I submitted a CL that made append, only clear > memory that was not going to be overwritten ( > https://github.com/golang/go/commit/c1e267cc734135a66af8a1a5015e572cbb598d44 > ). I thought this would have a much larger impact, but it only had a small > impact. memclr would zero the memory, but it also brought it into the > cache, where it was hot for being overwritten. > > Have you tried running with perf to see dcache misses for each benchmark? > > how to check cache misses with go pperf?
> On Wednesday, December 14, 2016 at 6:12:08 AM UTC-8, T L wrote: >> >> I just read this issue thread: https://github.com/golang/go/issues/5373 >> and this https://codereview.appspot.com/137880043 >> which says: >> >> for i := range a { >> a[i] = [zero val] >> } >> >> will be replaced with memclr. >> I made some benchmarks, but the results are disappointing. >> When the length of slice/array is very large, memclr is slower. >> >> Result >> >> BenchmarkMemclr_100-4 100000000 37.2 ns/op >> BenchmarkLoop_100-4 100000000 70.7 ns/op >> BenchmarkMemclr_1000-4 20000000 351 ns/op >> BenchmarkLoop_1000-4 10000000 464 ns/op >> BenchmarkMemclr_10000-4 1000000 3623 ns/op >> BenchmarkLoop_10000-4 1000000 4940 ns/op >> BenchmarkMemclr_100000-4 100000 49230 ns/op >> BenchmarkLoop_100000-4 100000 58761 ns/op >> BenchmarkMemclr_200000-4 50000 98165 ns/op >> BenchmarkLoop_200000-4 50000 115833 ns/op >> BenchmarkMemclr_300000-4 30000 170617 ns/op >> BenchmarkLoop_300000-4 20000 190193 ns/op >> BenchmarkMemclr_400000-4 20000 275676 ns/op >> BenchmarkLoop_400000-4 20000 288729 ns/op >> BenchmarkMemclr_500000-4 10000 410280 ns/op >> BenchmarkLoop_500000-4 10000 416195 ns/op >> BenchmarkMemclr_1000000-4 5000 1025504 ns/op >> BenchmarkLoop_1000000-4 5000 1012198 ns/op >> BenchmarkMemclr_2000000-4 2000 2071861 ns/op >> BenchmarkLoop_2000000-4 2000 2032703 ns/op >> >> test code: >> >> package main >> >> import "testing" >> >> func memclr(a []int) { >> for i := range a { >> a[i] = 0 >> } >> } >> >> func memsetLoop(a []int, v int) { >> for i := range a { >> a[i] = v >> } >> } >> >> var i = 0 >> >> func BenchmarkMemclr_100(b *testing.B) { >> var a = make([]int, 100) >> b.ResetTimer() >> for i := 0; i < b.N; i++ { >> memclr(a) >> } >> } >> >> func BenchmarkLoop_100(b *testing.B) { >> var a = make([]int, 100) >> b.ResetTimer() >> for i := 0; i < b.N; i++ { >> memsetLoop(a, i) >> } >> } >> >> func BenchmarkMemclr_1000(b *testing.B) { >> var a = make([]int, 1000) >> b.ResetTimer() >> for i := 0; i < b.N; i++ { >> memclr(a) >> } >> } >> >> func BenchmarkLoop_1000(b *testing.B) { >> var a = make([]int, 1000) >> b.ResetTimer() >> for i := 0; i < b.N; i++ { >> memsetLoop(a, i) >> } >> } >> >> func BenchmarkMemclr_10000(b *testing.B) { >> var a = make([]int, 10000) >> b.ResetTimer() >> for i := 0; i < b.N; i++ { >> memclr(a) >> } >> } >> >> func BenchmarkLoop_10000(b *testing.B) { >> var a = make([]int, 10000) >> b.ResetTimer() >> for i := 0; i < b.N; i++ { >> memsetLoop(a, i) >> } >> } >> >> func BenchmarkMemclr_100000(b *testing.B) { >> var a = make([]int, 100000) >> b.ResetTimer() >> for i := 0; i < b.N; i++ { >> memclr(a) >> } >> } >> >> func BenchmarkLoop_100000(b *testing.B) { >> var a = make([]int, 100000) >> b.ResetTimer() >> for i := 0; i < b.N; i++ { >> memsetLoop(a, i) >> } >> } >> >> func BenchmarkMemclr_200000(b *testing.B) { >> var a = make([]int, 200000) >> b.ResetTimer() >> for i := 0; i < b.N; i++ { >> memclr(a) >> } >> } >> >> func BenchmarkLoop_200000(b *testing.B) { >> var a = make([]int, 200000) >> b.ResetTimer() >> for i := 0; i < b.N; i++ { >> memsetLoop(a, i) >> } >> } >> >> func BenchmarkMemclr_300000(b *testing.B) { >> var a = make([]int, 300000) >> b.ResetTimer() >> for i := 0; i < b.N; i++ { >> memclr(a) >> } >> } >> >> func BenchmarkLoop_300000(b *testing.B) { >> var a = make([]int, 300000) >> b.ResetTimer() >> for i := 0; i < b.N; i++ { >> memsetLoop(a, i) >> } >> } >> >> func BenchmarkMemclr_400000(b *testing.B) { >> var a = make([]int, 400000) >> b.ResetTimer() >> for i := 0; i < b.N; i++ { >> memclr(a) >> } >> } >> >> func BenchmarkLoop_400000(b *testing.B) { >> var a = make([]int, 400000) >> b.ResetTimer() >> for i := 0; i < b.N; i++ { >> memsetLoop(a, i) >> } >> } >> >> func BenchmarkMemclr_500000(b *testing.B) { >> var a = make([]int, 500000) >> b.ResetTimer() >> for i := 0; i < b.N; i++ { >> memclr(a) >> } >> } >> >> func BenchmarkLoop_500000(b *testing.B) { >> var a = make([]int, 500000) >> b.ResetTimer() >> for i := 0; i < b.N; i++ { >> memsetLoop(a, i) >> } >> } >> >> func BenchmarkMemclr_1000000(b *testing.B) { >> var a = make([]int, 1000000) >> b.ResetTimer() >> for i := 0; i < b.N; i++ { >> memclr(a) >> } >> } >> >> func BenchmarkLoop_1000000(b *testing.B) { >> var a = make([]int, 1000000) >> b.ResetTimer() >> for i := 0; i < b.N; i++ { >> memsetLoop(a, i) >> } >> } >> >> func BenchmarkMemclr_2000000(b *testing.B) { >> var a = make([]int, 2000000) >> b.ResetTimer() >> for i := 0; i < b.N; i++ { >> memclr(a) >> } >> } >> >> func BenchmarkLoop_2000000(b *testing.B) { >> var a = make([]int, 2000000) >> b.ResetTimer() >> for i := 0; i < b.N; i++ { >> memsetLoop(a, i) >> } >> } >> >> >> >> >> -- 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. For more options, visit https://groups.google.com/d/optout.
