[dpdk-dev] [PATCH v2] ethdev: Prefetch driver variable structure

[Polehn, Mike A]

Adds ethdev driver prefetch of variable structure to CPU cache 0
while calling into tx or rx device driver operation.

RFC 2544 test of NIC task test measurement points show improvement
of lower latency and/or better packet throughput indicating clock
cycles saved.

Signed-off-by: Mike A. Polehn <mike.a.polehn at intel.com>
---
lib/librte_ether/rte_ethdev.h | 16 +++++++++++++---
1 file changed, 13 insertions(+), 3 deletions(-)

diff --git a/lib/librte_ether/rte_ethdev.h b/lib/librte_ether/rte_ethdev.h
index 48a540d..f1c35de 100644
--- a/lib/librte_ether/rte_ethdev.h
+++ b/lib/librte_ether/rte_ethdev.h
@@ -2458,12 +2458,17 @@ rte_eth_rx_burst(uint8_t port_id, uint16_t queue_id,
              struct rte_mbuf **rx_pkts, const uint16_t nb_pkts)
{
      struct rte_eth_dev *dev;
+      int16_t nb_rx;
       dev = &rte_eth_devices[port_id];
-      int16_t nb_rx = (*dev->rx_pkt_burst)(dev->data->rx_queues[queue_id],
-                    rx_pkts, nb_pkts);
+      { /* limit scope of rxq variable */
+             /* rxq is going to be immediately used, prefetch it */
+             void *rxq = dev->data->rx_queues[queue_id];
+             rte_prefetch0(rxq);
+             nb_rx = (*dev->rx_pkt_burst)(rxq, rx_pkts, nb_pkts);
+      }
#ifdef RTE_ETHDEV_RXTX_CALLBACKS
      struct rte_eth_rxtx_callback *cb = dev->post_rx_burst_cbs[queue_id];
@@ -2600,6 +2605,7 @@ rte_eth_tx_burst(uint8_t port_id, uint16_t queue_id,
              struct rte_mbuf **tx_pkts, uint16_t nb_pkts)
{
      struct rte_eth_dev *dev;
+      void *txq;
       dev = &rte_eth_devices[port_id];
@@ -2615,7 +2621,11 @@ rte_eth_tx_burst(uint8_t port_id, uint16_t queue_id,
      }
#endif
-      return (*dev->tx_pkt_burst)(dev->data->tx_queues[queue_id], tx_pkts, nb_pkts);
+      /* txq is going to be immediately used, prefetch it */
+      txq = dev->data->tx_queues[queue_id];
+      rte_prefetch0(txq);
+
+      return (*dev->tx_pkt_burst)(txq, tx_pkts, nb_pkts);
}
#endif
--
2.6.0