[dpdk-dev] [PATCH RFC 1/2] net/i40e: allow bulk alloc for the max size desc ring

[Ilya Maximets]

The only reason why bulk alloc disabled for the rings with
more than (I40E_MAX_RING_DESC - RTE_PMD_I40E_RX_MAX_BURST)
descriptors is the possible out-of-bound access to the dma
memory. But it's the artificial limit and can be easily
avoided by allocating of RTE_PMD_I40E_RX_MAX_BURST more
descriptors in memory. This will not interfere the HW and,
as soon as all rings' memory zeroized, Rx functions will
work correctly.

This change allows to use vectorized Rx functions with
4096 descriptors in Rx ring which is important to achieve
zero packet drop rate in high-load installations.

Signed-off-by: Ilya Maximets <i.maximets at samsung.com>
---
 drivers/net/i40e/i40e_rxtx.c | 24 +++++++++++++-----------
 1 file changed, 13 insertions(+), 11 deletions(-)

diff --git a/drivers/net/i40e/i40e_rxtx.c b/drivers/net/i40e/i40e_rxtx.c
index 7ae7d9f..1f76691 100644
--- a/drivers/net/i40e/i40e_rxtx.c
+++ b/drivers/net/i40e/i40e_rxtx.c
@@ -409,15 +409,6 @@ check_rx_burst_bulk_alloc_preconditions(__rte_unused struct i40e_rx_queue *rxq)
 			     "rxq->rx_free_thresh=%d",
 			     rxq->nb_rx_desc, rxq->rx_free_thresh);
 		ret = -EINVAL;
-	} else if (!(rxq->nb_rx_desc < (I40E_MAX_RING_DESC -
-				RTE_PMD_I40E_RX_MAX_BURST))) {
-		PMD_INIT_LOG(DEBUG, "Rx Burst Bulk Alloc Preconditions: "
-			     "rxq->nb_rx_desc=%d, "
-			     "I40E_MAX_RING_DESC=%d, "
-			     "RTE_PMD_I40E_RX_MAX_BURST=%d",
-			     rxq->nb_rx_desc, I40E_MAX_RING_DESC,
-			     RTE_PMD_I40E_RX_MAX_BURST);
-		ret = -EINVAL;
 	}
 #else
 	ret = -EINVAL;
@@ -1698,8 +1689,19 @@ i40e_dev_rx_queue_setup(struct rte_eth_dev *dev,
 	rxq->rx_deferred_start = rx_conf->rx_deferred_start;
 
 	/* Allocate the maximun number of RX ring hardware descriptor. */
-	ring_size = sizeof(union i40e_rx_desc) * I40E_MAX_RING_DESC;
-	ring_size = RTE_ALIGN(ring_size, I40E_DMA_MEM_ALIGN);
+	len = I40E_MAX_RING_DESC;
+
+#ifdef RTE_LIBRTE_I40E_RX_ALLOW_BULK_ALLOC
+	/**
+	 * Allocating a little more memory because vectorized/bulk_alloc Rx
+	 * functions doesn't check boundaries each time.
+	 */
+	len += RTE_PMD_I40E_RX_MAX_BURST;
+#endif
+
+	ring_size = RTE_ALIGN(len * sizeof(union i40e_rx_desc),
+			      I40E_DMA_MEM_ALIGN);
+
 	rz = rte_eth_dma_zone_reserve(dev, "rx_ring", queue_idx,
 			      ring_size, I40E_RING_BASE_ALIGN, socket_id);
 	if (!rz) {
-- 
2.7.4