runtime: avoid memclr call for keys in mapdelete_fast
Replace memclrHasPointers calls for keys in mapdelete_fast*
functions with direct writes since the key sizes are known
at compile time.
name old time/op new time/op delta
MapDelete/Pointer/100 33.7ns ± 1% 23.7ns ± 2% -29.68% (p=0.000 n=7+9)
MapDelete/Pointer/1000 41.6ns ± 5% 34.9ns ± 4% -16.01% (p=0.000 n=9+10)
MapDelete/Pointer/10000 45.6ns ± 1% 38.2ns ± 2% -16.34% (p=0.000 n=8+10)
Change-Id: Icaac43b520b93c2cf9fd192b822fae7203a7bbf7
Reviewed-on: https://go-review.googlesource.com/c/go/+/231737
Run-TryBot: Martin Möhrmann <moehrmann@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
diff --git a/src/runtime/map_fast32.go b/src/runtime/map_fast32.go
index 534454f..d035ed0 100644
--- a/src/runtime/map_fast32.go
+++ b/src/runtime/map_fast32.go
@@ -299,8 +299,12 @@
continue
}
// Only clear key if there are pointers in it.
- if t.key.ptrdata != 0 {
- memclrHasPointers(k, t.key.size)
+ // This can only happen if pointers are 32 bit
+ // wide as 64 bit pointers do not fit into a 32 bit key.
+ if sys.PtrSize == 4 && t.key.ptrdata != 0 {
+ // The key must be a pointer as we checked pointers are
+ // 32 bits wide and the key is 32 bits wide also.
+ *(*unsafe.Pointer)(k) = nil
}
e := add(unsafe.Pointer(b), dataOffset+bucketCnt*4+i*uintptr(t.elemsize))
if t.elem.ptrdata != 0 {
diff --git a/src/runtime/map_fast64.go b/src/runtime/map_fast64.go
index 1669c7c..f1f3927 100644
--- a/src/runtime/map_fast64.go
+++ b/src/runtime/map_fast64.go
@@ -300,7 +300,13 @@
}
// Only clear key if there are pointers in it.
if t.key.ptrdata != 0 {
- memclrHasPointers(k, t.key.size)
+ if sys.PtrSize == 8 {
+ *(*unsafe.Pointer)(k) = nil
+ } else {
+ // There are three ways to squeeze at one ore more 32 bit pointers into 64 bits.
+ // Just call memclrHasPointers instead of trying to handle all cases here.
+ memclrHasPointers(k, 8)
+ }
}
e := add(unsafe.Pointer(b), dataOffset+bucketCnt*8+i*uintptr(t.elemsize))
if t.elem.ptrdata != 0 {
diff --git a/src/runtime/map_test.go b/src/runtime/map_test.go
index 1b7ccad..302b3c2 100644
--- a/src/runtime/map_test.go
+++ b/src/runtime/map_test.go
@@ -993,6 +993,27 @@
}
}
+func benchmarkMapDeletePointer(b *testing.B, n int) {
+ i2p := make([]*int, n)
+ for i := 0; i < n; i++ {
+ i2p[i] = new(int)
+ }
+ a := make(map[*int]int, n)
+ b.ResetTimer()
+ k := 0
+ for i := 0; i < b.N; i++ {
+ if len(a) == 0 {
+ b.StopTimer()
+ for j := 0; j < n; j++ {
+ a[i2p[j]] = j
+ }
+ k = i
+ b.StartTimer()
+ }
+ delete(a, i2p[i-k])
+ }
+}
+
func runWith(f func(*testing.B, int), v ...int) func(*testing.B) {
return func(b *testing.B) {
for _, n := range v {
@@ -1023,6 +1044,7 @@
b.Run("Int32", runWith(benchmarkMapDeleteInt32, 100, 1000, 10000))
b.Run("Int64", runWith(benchmarkMapDeleteInt64, 100, 1000, 10000))
b.Run("Str", runWith(benchmarkMapDeleteStr, 100, 1000, 10000))
+ b.Run("Pointer", runWith(benchmarkMapDeletePointer, 100, 1000, 10000))
}
func TestDeferDeleteSlow(t *testing.T) {
