map: avoid copy in appendPerCPUSlice

Signed-off-by: Lorenz Bauer <[email protected]>

Author: lmb

internal/sysenc/buffer.go

@@ -54,6 +54,11 @@ func (b Buffer) CopyTo(dst []byte) int {
 	return copy(dst, b.unsafeBytes())
 }
 
+// AppendTo appends the buffer onto dst.
+func (b Buffer) AppendTo(dst []byte) []byte {
+	return append(dst, b.unsafeBytes()...)
+}
+
 // Pointer returns the location where a syscall should write.
 func (b Buffer) Pointer() sys.Pointer {
 	// NB: This deliberately ignores b.length to support zero-copy

marshalers.go

@@ -70,14 +70,13 @@ func appendPerCPUSlice(buf []byte, slice any, possibleCPUs, elemLength, alignedE
 			return nil, err
 		}
 
-		elemBytes.CopyTo(buf[len(buf) : len(buf)+elemLength]) // Only copies elemLength
-		buf = buf[:len(buf)+alignedElemLength]
+		buf = elemBytes.AppendTo(buf)
+		buf = append(buf, make([]byte, alignedElemLength-elemLength)...)
 	}
+
 	// Ensure buf is zero-padded full size.
-	for i := 0; i < possibleCPUs-sliceLen; i++ {
-		b := make([]byte, alignedElemLength)
-		buf = append(buf, b...)
-	}
+	buf = append(buf, make([]byte, (possibleCPUs-sliceLen)*alignedElemLength)...)
+
 	return buf, nil
 }