[dpdk-dev] [PATCH v2 4/5] net/ena: fix Tx sq free space assessment

[Michal Krawczyk <mk@semihalf.com>]

From: Igor Chauskin <igorch@amazon.com>

Before starting transmission of Tx burst, the driver checked the
available space in the sq and limited the number of packets for
transmission accordingly.
The calculation was incorrect for fragmented packets and potentially had
significantly limited the length of Tx bursts.

This patch removes the assessment and pushes packets to the sq as long
as the burst is not exhausted and space is available in the sq.

Correct evaluation of the required space isn't possible before the burst
because it depends on the number of segments of each packet.
This patch adds per-packet space evaluation for each packet before
attempting to process it. In case there is not enough queue space, the
burst will just stop without error.

Signed-off-by: Igor Chauskin <igorch@amazon.com>
Reviewed-by: Michal Krawczyk <mk@semihalf.com>
---
 drivers/net/ena/ena_ethdev.c | 35 ++++++++++++++++++++++++++---------
 1 file changed, 26 insertions(+), 9 deletions(-)

diff --git a/drivers/net/ena/ena_ethdev.c b/drivers/net/ena/ena_ethdev.c
index 9ee9de6eb9..4083568d5d 100644
--- a/drivers/net/ena/ena_ethdev.c
+++ b/drivers/net/ena/ena_ethdev.c
@@ -2359,8 +2359,8 @@ static void ena_update_hints(struct ena_adapter *adapter,
 	}
 }
 
-static int ena_check_and_linearize_mbuf(struct ena_ring *tx_ring,
-					struct rte_mbuf *mbuf)
+static int ena_check_space_and_linearize_mbuf(struct ena_ring *tx_ring,
+					      struct rte_mbuf *mbuf)
 {
 	struct ena_com_dev *ena_dev;
 	int num_segments, header_len, rc;
@@ -2370,13 +2370,21 @@ static int ena_check_and_linearize_mbuf(struct ena_ring *tx_ring,
 	header_len = mbuf->data_len;
 
 	if (likely(num_segments < tx_ring->sgl_size))
-		return 0;
+		goto checkspace;
 
 	if (ena_dev->tx_mem_queue_type == ENA_ADMIN_PLACEMENT_POLICY_DEV &&
 	    (num_segments == tx_ring->sgl_size) &&
 	    (header_len < tx_ring->tx_max_header_size))
-		return 0;
+		goto checkspace;
 
+	/* Checking for space for 2 additional metadata descriptors due to
+	 * possible header split and metadata descriptor. Linearization will
+	 * be needed so we reduce the segments number from num_segments to 1
+	 */
+	if (!ena_com_sq_have_enough_space(tx_ring->ena_com_io_sq, 3)) {
+		PMD_DRV_LOG(DEBUG, "Not enough space in the tx queue\n");
+		return ENA_COM_NO_MEM;
+	}
 	++tx_ring->tx_stats.linearize;
 	rc = rte_pktmbuf_linearize(mbuf);
 	if (unlikely(rc)) {
@@ -2386,7 +2394,19 @@ static int ena_check_and_linearize_mbuf(struct ena_ring *tx_ring,
 		return rc;
 	}
 
-	return rc;
+	return 0;
+
+checkspace:
+	/* Checking for space for 2 additional metadata descriptors due to
+	 * possible header split and metadata descriptor
+	 */
+	if (!ena_com_sq_have_enough_space(tx_ring->ena_com_io_sq,
+					  num_segments + 2)) {
+		PMD_DRV_LOG(DEBUG, "Not enough space in the tx queue\n");
+		return ENA_COM_NO_MEM;
+	}
+
+	return 0;
 }
 
 static void ena_tx_map_mbuf(struct ena_ring *tx_ring,
@@ -2473,7 +2493,7 @@ static int ena_xmit_mbuf(struct ena_ring *tx_ring, struct rte_mbuf *mbuf)
 	int nb_hw_desc;
 	int rc;
 
-	rc = ena_check_and_linearize_mbuf(tx_ring, mbuf);
+	rc = ena_check_space_and_linearize_mbuf(tx_ring, mbuf);
 	if (unlikely(rc))
 		return rc;
 
@@ -2580,9 +2600,6 @@ static uint16_t eth_ena_xmit_pkts(void *tx_queue, struct rte_mbuf **tx_pkts,
 		return 0;
 	}
 
-	nb_pkts = RTE_MIN(ena_com_free_q_entries(tx_ring->ena_com_io_sq),
-		nb_pkts);
-
 	for (sent_idx = 0; sent_idx < nb_pkts; sent_idx++) {
 		if (ena_xmit_mbuf(tx_ring, tx_pkts[sent_idx]))
 			break;
-- 
2.25.1