Make packet cache cache-friendly.

packetcache/packetcache.go

@@ -8,8 +8,9 @@ const BufSize = 1500
 
 type entry struct {
 	seqno  uint16
-	length int
+	length uint16
 	buf    [BufSize]byte
+	pad    [32 - (BufSize+4)%32]byte // avoid false sharing
 }
 
 type Cache struct {
@@ -99,7 +100,7 @@ func (cache *Cache) Store(seqno uint16, buf []byte) uint16 {
 
 	cache.entries[cache.tail].seqno = seqno
 	copy(cache.entries[cache.tail].buf[:], buf)
-	cache.entries[cache.tail].length = len(buf)
+	cache.entries[cache.tail].length = uint16(len(buf))
 	cache.tail = (cache.tail + 1) % len(cache.entries)
 
 	return cache.first

packetcache/packetcache_test.go

@@ -4,6 +4,7 @@ import (
 	"bytes"
 	"math/rand"
 	"testing"
+	"unsafe"
 
 	"github.com/pion/rtcp"
 )
@@ -54,6 +55,16 @@ func TestCacheOverflow(t *testing.T) {
 	}
 }
 
+func TestCacheAlignment(t *testing.T) {
+	cache := New(16)
+	for i := range cache.entries {
+		p := unsafe.Pointer(&cache.entries[i])
+		if uintptr(p) % 32 != 0 {
+			t.Errorf("%v: alignment %v", i, uintptr(p) % 32)
+		}
+	}
+}
+
 func TestBitmap(t *testing.T) {
 	value := uint64(0xcdd58f1e035379c0)
 	packet := make([]byte, 1)