Index: sys/net/iflib.c
===================================================================
--- sys/net/iflib.c
+++ sys/net/iflib.c
@@ -586,8 +586,11 @@
 static int iflib_no_tx_batch = 0;
 SYSCTL_INT(_net_iflib, OID_AUTO, no_tx_batch, CTLFLAG_RW,
 		   &iflib_no_tx_batch, 0, "minimize transmit latency at the possible expense of throughput");
+int iflib_tx_update_freq = IFLIB_DEFAULT_TX_UPDATE_FREQ;
+SYSCTL_UINT(_net_iflib, OID_AUTO, tx_update_freq, CTLFLAG_RWTUN,
+		   &iflib_tx_update_freq, IFLIB_DEFAULT_TX_UPDATE_FREQ,
+		   "tramsmit descriptor updates per second");
 
-
 #if IFLIB_DEBUG_COUNTERS
 
 static int iflib_tx_seen;
@@ -1768,8 +1771,7 @@
 
 	/* Set number of descriptors available */
 	txq->ift_qstatus = IFLIB_QUEUE_IDLE;
-	/* XXX make configurable */
-	txq->ift_update_freq = IFLIB_DEFAULT_TX_UPDATE_FREQ;
+	txq->ift_update_freq = iflib_tx_update_freq;
 
 	/* Reset indices */
 	txq->ift_cidx_processed = 0;