In bce_start_locked, check the used_tx_bd count rather than the

descriptor's mbuf pointer to see if the transmit ring is full.  The
mbuf pointer is set only in the last descriptor of a
multi-descriptor packet.  By relying on the mbuf pointers of the
earlier descriptors, the driver would sometimes overwrite a
descriptor belonging to a packet that wasn't completed yet.  Also,
tx_chain_prod wasn't updated inside the loop, causing the wrong
descriptor to be checked after the first iteration.  The upshot of
all this was the loss of some transmitted packets at medium to high
packet rates.

In bce_tx_encap, remove a couple of old statements that shuffled
around the tx_mbuf_map pointers.  These now correspond 1-to-1 with
the transmit descriptors, and they are not supposed to be changed.

Correct a couple of inaccurate comments.

MFC after:	1 month

1 files changed, 8 insertions, 8 deletions

diff --git a/sys/dev/bce/if_bce.c b/sys/dev/bce/if_bce.c
index 2b67c43adc05..7f09135b8c7d 100644
--- a/sys/dev/bce/if_bce.c
+++ b/sys/dev/bce/if_bce.c
@@ -4652,17 +4652,14 @@ bce_tx_encap(struct bce_softc *sc, struct mbuf **m_head)
 		__FUNCTION__, prod, chain_prod, prod_bseq);
 
 	/*
-	 * Ensure that the map for this transmission
+	 * Ensure that the mbuf pointer for this transmission
 	 * is placed at the array index of the last
 	 * descriptor in this chain.  This is done
 	 * because a single map is used for all 
 	 * segments of the mbuf and we don't want to
-	 * delete the map before all of the segments
+	 * unload the map before all of the segments
 	 * have been freed.
 	 */
-	sc->tx_mbuf_map[TX_CHAIN_IDX(sc->tx_prod)] = 
-		sc->tx_mbuf_map[chain_prod];
-	sc->tx_mbuf_map[chain_prod] = map;
 	sc->tx_mbuf_ptr[chain_prod] = m0;
 	sc->used_tx_bd += nsegs;
 
@@ -4673,7 +4670,7 @@ bce_tx_encap(struct bce_softc *sc, struct mbuf **m_head)
 
 	DBRUN(BCE_VERBOSE_SEND, bce_dump_tx_mbuf_chain(sc, chain_prod, nsegs));
 
-	/* prod still points the last used tx_bd at this point. */
+	/* prod points to the next free tx_bd at this point. */
 	sc->tx_prod = prod;
 	sc->tx_prod_bseq = prod_bseq;
 
@@ -4711,8 +4708,11 @@ bce_start_locked(struct ifnet *ifp)
 		"tx_prod_bseq = 0x%08X\n",
 		__FUNCTION__, tx_prod, tx_chain_prod, sc->tx_prod_bseq);
 
-	/* Keep adding entries while there is space in the ring. */
-	while (sc->tx_mbuf_ptr[tx_chain_prod] == NULL) {
+	/*
+	 * Keep adding entries while there is space in the ring.  We keep
+	 * BCE_TX_SLACK_SPACE entries unused at all times.
+	 */
+	while (sc->used_tx_bd < USABLE_TX_BD - BCE_TX_SLACK_SPACE) {
 
 		/* Check for any frames to send. */
 		IFQ_DRV_DEQUEUE(&ifp->if_snd, m_head);