Repository navigation
maps: Performance Regression in maps.Clone after Go 1.24 Refactor #72983
Description
Go 1.24 refactored the map runtime using SwissTable.
When I was using Go 1.24, I found that,
compared to using a for loop to copy a map,
the performance of the built-in maps.Clone was actually worse.
At the same time, in versions prior to Go 1.24,
the performance of maps.Clone was the best.
Below is the code I used for performance testing:
package clone
import (
"maps"
"testing"
)
func clone1(m map[string]string) map[string]string {
if m == nil {
return nil
}
m2 := make(map[string]string, len(m))
for k, v := range m {
m2[k] = v
}
return m2
}
func clone2[M ~map[K]V, K comparable, V any](m M) M {
if m == nil {
return nil
}
m2 := make(M, len(m))
for k, v := range m {
m2[k] = v
}
return m2
}
var m = map[string]string{
"k1": "v1",
"k2": "v2",
"k3": "v3",
"k4": "v4",
}
func BenchmarkClone1(b *testing.B) {
for i := 0; i < b.N; i++ {
clone1(m)
}
}
func BenchmarkClone2(b *testing.B) {
for i := 0; i < b.N; i++ {
clone2(m)
}
}
func BenchmarkStdClone(b *testing.B) {
for i := 0; i < b.N; i++ {
maps.Clone(m)
}
}Performance test results for different Go versions are as follows:
Go 1.24
goos: darwin
goarch: arm64
pkg: test_code/test_map/clone
cpu: Apple M3 Pro
BenchmarkClone1
BenchmarkClone1-11 16550962 72.64 ns/op
BenchmarkClone2
BenchmarkClone2-11 16820404 71.59 ns/op
BenchmarkStdClone
BenchmarkStdClone-11 9009817 134.1 ns/op
PASS
Process finished with the exit code 0
Go 1.23
goos: darwin
goarch: arm64
pkg: test_code/test_map/clone
cpu: Apple M3 Pro
BenchmarkClone1
BenchmarkClone1-11 15726506 77.62 ns/op
BenchmarkClone2
BenchmarkClone2-11 14940602 80.03 ns/op
BenchmarkStdClone
BenchmarkStdClone-11 20451465 59.58 ns/op
PASS
Process finished with the exit code 0
The results for Go 1.22 and Go 1.21 are similar to Go 1.23.
Activity
gabyhelp commentedon Mar 21, 2025
Related Issues
Related Code Changes
(Emoji vote if this was helpful or unhelpful; more detailed feedback welcome in this discussion.)
seankhliao commentedon Mar 21, 2025
That benchmark looks invalid, the return value is discarded and can be optimized away.
Ensuring the value is retained produces more consistent results: https://go.dev/play/p/jBtvROSBTzV
1911860538 commentedon Mar 21, 2025
I conducted benchmarks for Go 1.23 and Go 1.24 locally based on your code.
Below is the test code. Using the same test code, I tested it with Go 1.24 and Go 1.23 separately.
For the same maps.Clone code, the execution speed in Go 1.23 is twice that of Go 1.24.
clone_test.go
Go1.24 output
Go1.23 output
mateusz834 commentedon Mar 21, 2025
AFAIAC in
go1.24themaps.Cloneis not optimized specially as it was for non-swiss maps in 1.23(#70836)
1911860538 commentedon Mar 21, 2025
So the performance regression of
maps.Cloneis a fact.