[RFC PATCH 10/14] mbuf: set next pointer to NULL on mbuf free.

[Bruce Richardson <bruce.richardson-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>]

Previously we set the next pointer to NULL on allocation, we now set it
to NULL on free, as the next pointer is on a second cache line.

Signed-off-by: Bruce Richardson <bruce.richardson-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
---
 lib/librte_mbuf/rte_mbuf.h        |  4 +++-
 lib/librte_pmd_ixgbe/ixgbe_rxtx.c | 18 +++++++++---------
 2 files changed, 12 insertions(+), 10 deletions(-)

diff --git a/lib/librte_mbuf/rte_mbuf.h b/lib/librte_mbuf/rte_mbuf.h
index a3e3e4f..01d4f6e 100644
--- a/lib/librte_mbuf/rte_mbuf.h
+++ b/lib/librte_mbuf/rte_mbuf.h
@@ -629,8 +629,10 @@ __rte_pktmbuf_prefree_seg(struct rte_mbuf *m)
 static inline void __attribute__((always_inline))
 rte_pktmbuf_free_seg(struct rte_mbuf *m)
 {
-	if (likely(NULL != (m = __rte_pktmbuf_prefree_seg(m))))
+	if (likely(NULL != (m = __rte_pktmbuf_prefree_seg(m)))) {
+		m->next = NULL;
 		__rte_mbuf_raw_free(m);
+	}
 }
 
 /**
diff --git a/lib/librte_pmd_ixgbe/ixgbe_rxtx.c b/lib/librte_pmd_ixgbe/ixgbe_rxtx.c
index fa3b357..f9cc352 100644
--- a/lib/librte_pmd_ixgbe/ixgbe_rxtx.c
+++ b/lib/librte_pmd_ixgbe/ixgbe_rxtx.c
@@ -145,6 +145,7 @@ ixgbe_tx_free_bufs(struct igb_tx_queue *txq)
 	/* free buffers one at a time */
 	if ((txq->txq_flags & (uint32_t)ETH_TXQ_FLAGS_NOREFCOUNT) != 0) {
 		for (i = 0; i < txq->tx_rs_thresh; ++i, ++txep) {
+			txep->mbuf->next = NULL;
 			rte_mempool_put(txep->mbuf->pool, txep->mbuf);
 			txep->mbuf = NULL;
 		}
@@ -250,6 +251,14 @@ tx_xmit_pkts(void *tx_queue, struct rte_mbuf **tx_pkts,
 	volatile union ixgbe_adv_tx_desc *tx_r = txq->tx_ring;
 	uint16_t n = 0;
 
+	/*
+	 * Begin scanning the H/W ring for done descriptors when the
+	 * number of available descriptors drops below tx_free_thresh.  For
+	 * each done descriptor, free the associated buffer.
+	 */
+	if (txq->nb_tx_free < txq->tx_free_thresh)
+		ixgbe_tx_free_bufs(txq);
+
 	/* Only use descriptors that are available */
 	nb_pkts = (uint16_t)RTE_MIN(txq->nb_tx_free, nb_pkts);
 	if (unlikely(nb_pkts == 0))
@@ -313,15 +322,6 @@ tx_xmit_pkts(void *tx_queue, struct rte_mbuf **tx_pkts,
 	if (txq->tx_tail >= txq->nb_tx_desc)
 		txq->tx_tail = 0;
 
-	/*
-	 * Begin scanning the H/W ring for done descriptors when the
-	 * number of available descriptors drops below tx_free_thresh.  For
-	 * each done descriptor, free the associated buffer.
-	 */
-	if (txq->nb_tx_free < txq->tx_free_thresh)
-		ixgbe_tx_free_bufs(txq);
-
-
 	/* update tail pointer */
 	rte_wmb();
 	IXGBE_PCI_REG_WRITE(txq->tdt_reg_addr, txq->tx_tail);
-- 
1.9.3