[PATCH v3 03/10] net/gve: fix DQO Tx report event interval

[Tathagat Priyadarshi]

A descriptor completion is requested once every 32 packets, and Tx
descriptors are only reclaimed on these completions. With
multi-segment or TSO packets the ring can fill before 32 packets are
posted, so no completion is ever requested and the Tx queue stalls
for good.

Request a completion once GVE_TX_MIN_RE_INTERVAL descriptors have
been posted since the last one, as the Linux driver does.

Fixes: 4022f9999f56 ("net/gve: support basic Tx data path for DQO")
Fixes: 403c671a46b6 ("net/gve: support TSO in DQO RDA")
Cc: stable at dpdk.org

Signed-off-by: Tathagat Priyadarshi <tathagat.dpdk at gmail.com>
---
 drivers/net/gve/gve_ethdev.h |  2 +-
 drivers/net/gve/gve_tx_dqo.c | 22 ++++++++++++++--------
 2 files changed, 15 insertions(+), 9 deletions(-)

diff --git a/drivers/net/gve/gve_ethdev.h b/drivers/net/gve/gve_ethdev.h
index c9a176ff17..8349b1c92e 100644
--- a/drivers/net/gve/gve_ethdev.h
+++ b/drivers/net/gve/gve_ethdev.h
@@ -194,7 +194,7 @@ struct gve_tx_queue {
 	uint8_t cur_gen_bit;
 	uint32_t last_desc_cleaned;
 	void **txqs;
-	uint16_t re_cnt;
+	uint16_t last_re_idx;
 
 	/* Only valid for DQO_RDA queue format */
 	struct gve_tx_queue *complq;
diff --git a/drivers/net/gve/gve_tx_dqo.c b/drivers/net/gve/gve_tx_dqo.c
index c864d722d9..a2ebadd0b8 100644
--- a/drivers/net/gve/gve_tx_dqo.c
+++ b/drivers/net/gve/gve_tx_dqo.c
@@ -254,6 +254,8 @@ gve_tx_burst_dqo(void *tx_queue, struct rte_mbuf **tx_pkts, uint16_t nb_pkts)
 	volatile union gve_tx_desc_dqo *txr;
 	volatile union gve_tx_desc_dqo *txd;
 	uint16_t mask = txq->nb_tx_desc - 1;
+	uint16_t last_re_interval;
+	uint16_t last_desc_idx;
 	struct gve_tx_pkt *pkts;
 	struct rte_mbuf *tx_pkt;
 	uint16_t compl_tag;
@@ -331,20 +333,23 @@ gve_tx_burst_dqo(void *tx_queue, struct rte_mbuf **tx_pkts, uint16_t nb_pkts)
 		txd = &txr[(tx_id - 1) & mask];
 		txd->pkt.end_of_packet = 1;
 
+		/* Request a descriptor completion once at least
+		 * GVE_TX_MIN_RE_INTERVAL descriptors have been posted
+		 * since the last request.
+		 */
+		last_desc_idx = (tx_id - 1) & mask;
+		last_re_interval = (last_desc_idx - txq->last_re_idx) & mask;
+		if (unlikely(last_re_interval >= GVE_TX_MIN_RE_INTERVAL)) {
+			txd->pkt.report_event = true;
+			txq->last_re_idx = last_desc_idx;
+		}
+
 		txq->nb_free -= nb_descs;
 		txq->nb_used += nb_descs;
 	}
 
 	/* update the tail pointer if any packets were processed */
 	if (nb_tx > 0) {
-		/* Request a descriptor completion on the last descriptor */
-		txq->re_cnt += nb_tx;
-		if (txq->re_cnt >= GVE_TX_MIN_RE_INTERVAL) {
-			txd = &txr[(tx_id - 1) & mask];
-			txd->pkt.report_event = true;
-			txq->re_cnt = 0;
-		}
-
 		rte_write32(tx_id, txq->qtx_tail);
 		txq->tx_tail = tx_id;
 
@@ -445,6 +450,7 @@ gve_reset_tx_ring_state_dqo(struct gve_tx_queue *txq)
 	txq->nb_used = 0;
 
 	txq->last_desc_cleaned = 0;
+	txq->last_re_idx = 0;
 	txq->nb_free = txq->nb_tx_desc - 1;
 
 	txq->complq_tail = 0;
-- 
2.43.0