[dpdk-dev] [Patch 2/2] i40e simple tx: Larger list size (33 to 128) throughput optimization

[Polehn, Mike A]

Added packet memory prefetch for faster access to variables inside packet 
buffer needed 
for the free operation.

Signed-off-by: Mike A. Polehn <mike.a.polehn at intel.com>

diff --git a/drivers/net/i40e/i40e_rxtx.c b/drivers/net/i40e/i40e_rxtx.c
index 177fb2e..d9bc30a 100644
--- a/drivers/net/i40e/i40e_rxtx.c
+++ b/drivers/net/i40e/i40e_rxtx.c
@@ -1748,7 +1748,8 @@ static inline int __attribute__((always_inline))
 i40e_tx_free_bufs(struct i40e_tx_queue *txq)
 {
        struct i40e_tx_entry *txep;
-       uint16_t i;
+       unsigned i, l, tx_rs_thresh;
+       struct rte_mbuf *pk, *pk_next;

        if ((txq->tx_ring[txq->tx_next_dd].cmd_type_offset_bsz &
                        rte_cpu_to_le_64(I40E_TXD_QW1_DTYPE_MASK)) !=
@@ -1757,18 +1758,46 @@ i40e_tx_free_bufs(struct i40e_tx_queue *txq)

        txep = &(txq->sw_ring[txq->tx_next_dd - (txq->tx_rs_thresh - 1)]);

-       for (i = 0; i < txq->tx_rs_thresh; i++)
-               rte_prefetch0((txep + i)->mbuf);
+       /* Prefetch first 2 packets */
+       pk = txep->mbuf;
+       rte_prefetch0(pk);
+       txep->mbuf = NULL;
+       txep++;
+       tx_rs_thresh = txq->tx_rs_thresh;
+       if (likely(txq->tx_rs_thresh > 1)) {
+               pk_next = txep->mbuf;
+               rte_prefetch0(pk_next);
+               txep->mbuf = NULL;
+               txep++;
+               l = tx_rs_thresh - 2;
+       } else {
+               pk_next = pk;
+               l = tx_rs_thresh - 1;
+       }

        if (!(txq->txq_flags & (uint32_t)ETH_TXQ_FLAGS_NOREFCOUNT)) {
-               for (i = 0; i < txq->tx_rs_thresh; ++i, ++txep) {
-                       rte_mempool_put(txep->mbuf->pool, txep->mbuf);
-                       txep->mbuf = NULL;
+               for (i = 0; i < tx_rs_thresh; ++i) {
+                       struct rte_mbuf *mbuf = pk;
+                       pk = pk_next;
+                       if (likely(i < l)) {
+                               pk_next = txep->mbuf;
+                               rte_prefetch0(pk_next);
+                               txep->mbuf = NULL;
+                               txep++;
+                       }
+                       rte_mempool_put(mbuf->pool, mbuf);
                }
        } else {
-               for (i = 0; i < txq->tx_rs_thresh; ++i, ++txep) {
-                       rte_pktmbuf_free_seg(txep->mbuf);
-                       txep->mbuf = NULL;
+               for (i = 0; i < tx_rs_thresh; ++i) {
+                       struct rte_mbuf *mbuf = pk;
+                       pk = pk_next;
+                       if (likely(i < l)) {
+                               pk_next = txep->mbuf;
+                               rte_prefetch0(pk_next);
+                               txep->mbuf = NULL;
+                               txep++;
+                       }
+                       rte_pktmbuf_free_seg(mbuf);
                }
        }