[dpdk-dev] [PATCH 2/5] ixgbe: add prefetch to improve slow-path tx perf

[Bruce Richardson]

Make a small improvement to slow path TX performance by adding in a
prefetch for the second mbuf cache line.
Also move assignment of l2/l3 length values only when needed.

Signed-off-by: Bruce Richardson <bruce.richardson at intel.com>
---
 lib/librte_pmd_ixgbe/ixgbe_rxtx.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/lib/librte_pmd_ixgbe/ixgbe_rxtx.c 
b/lib/librte_pmd_ixgbe/ixgbe_rxtx.c
index 6f702b3..c0bb49f 100644
--- a/lib/librte_pmd_ixgbe/ixgbe_rxtx.c
+++ b/lib/librte_pmd_ixgbe/ixgbe_rxtx.c
@@ -565,25 +565,26 @@ ixgbe_xmit_pkts(void *tx_queue, struct rte_mbuf **tx_pkts,
                ixgbe_xmit_cleanup(txq);
        }

+       rte_prefetch0(&txe->mbuf->pool);
+
        /* TX loop */
        for (nb_tx = 0; nb_tx < nb_pkts; nb_tx++) {
                new_ctx = 0;
                tx_pkt = *tx_pkts++;
                pkt_len = tx_pkt->pkt_len;

-               RTE_MBUF_PREFETCH_TO_FREE(txe->mbuf);
-
                /*
                 * Determine how many (if any) context descriptors
                 * are needed for offload functionality.
                 */
                ol_flags = tx_pkt->ol_flags;
-               vlan_macip_lens.f.vlan_tci = tx_pkt->vlan_tci;
-               vlan_macip_lens.f.l2_l3_len = tx_pkt->l2_l3_len;

                /* If hardware offload required */
                tx_ol_req = ol_flags & PKT_TX_OFFLOAD_MASK;
                if (tx_ol_req) {
+                       vlan_macip_lens.f.vlan_tci = tx_pkt->vlan_tci;
+                       vlan_macip_lens.f.l2_l3_len = tx_pkt->l2_l3_len;
+
                        /* If new context need be built or reuse the exist ctx. 
*/
                        ctx = what_advctx_update(txq, tx_ol_req,
                                vlan_macip_lens.data);
@@ -720,7 +721,7 @@ ixgbe_xmit_pkts(void *tx_queue, struct rte_mbuf **tx_pkts,
                                    &txr[tx_id];

                                txn = &sw_ring[txe->next_id];
-                               RTE_MBUF_PREFETCH_TO_FREE(txn->mbuf);
+                               rte_prefetch0(&txn->mbuf->pool);

                                if (txe->mbuf != NULL) {
                                        rte_pktmbuf_free_seg(txe->mbuf);
@@ -749,6 +750,7 @@ ixgbe_xmit_pkts(void *tx_queue, struct rte_mbuf **tx_pkts,
                do {
                        txd = &txr[tx_id];
                        txn = &sw_ring[txe->next_id];
+                       rte_prefetch0(&txn->mbuf->pool);

                        if (txe->mbuf != NULL)
                                rte_pktmbuf_free_seg(txe->mbuf);
-- 
1.9.3