Cycle every payload pattern per packet and always run both directions

tx.go

@@ -24,10 +24,14 @@ type txWorker struct {
 }
 
 func (w *txWorker) run(done *atomic.Bool) {
+	// The batch is not a multiple of the pattern count, so the pairing of pattern
+	// to size rotates every pass rather than settling into a fixed one.
 	bufs := make([][]byte, w.batch)
+	pats := make([]int, w.batch)
 	for i := range bufs {
 		bufs[i] = make([]byte, w.spec.maxSize)
-		w.spec.prefill(bufs[i])
+		pats[i] = i % len(patterns)
+		w.spec.prefill(bufs[i], pats[i])
 	}
 	hdrs, iovs := newMmsghdrs(bufs)
 	sizes := make([]int, w.batch)
@@ -44,7 +48,8 @@ func (w *txWorker) run(done *atomic.Bool) {
 				si = 0
 			}
 			sizes[i] = size
-			putHeader(bufs[i], w.spec.patIdx, w.stream, seq+uint64(i), size-minFrame, w.spec.crcFor[size])
+			putHeader(bufs[i], pats[i], w.stream, seq+uint64(i), size-minFrame,
+				w.spec.crcFor[pats[i]][size])
 			iovs[i].Len = uint64(size)
 		}