[dpdk-dev] [PATCH] net/mlx5: fix mbufs overflow in vectorized MPRQ

[Alexander Kozyrev <akozyrev@nvidia.com>]

Changing the allocation scheme to improve mbufs locality caused mbufs
overrun in some cases. Revert the previous replenish logic back.
Calculate a number of unused mbufs and replenish max this number of mbufs.

Mark the last 4 mbufs as fake mbufs to prevent overflowing into consumed
mbufs in the future. Keep the consumed index and the produced index 4 mbufs
apart for this purpose.

Replenish some mbufs only in case the consumed index is within the
replenish threshold of the produced index in order to retain the cache
locality for the vectorized MPRQ routine.

Fixes: 5c68764377 ("net/mlx5: improve vectorized MPRQ descriptors locality")

Signed-off-by: Alexander Kozyrev <akozyrev@nvidia.com>
---
 drivers/net/mlx5/mlx5_rxtx_vec.c | 17 ++++++++++++-----
 1 file changed, 12 insertions(+), 5 deletions(-)

diff --git a/drivers/net/mlx5/mlx5_rxtx_vec.c b/drivers/net/mlx5/mlx5_rxtx_vec.c
index 68c51dce31..028e0f6121 100644
--- a/drivers/net/mlx5/mlx5_rxtx_vec.c
+++ b/drivers/net/mlx5/mlx5_rxtx_vec.c
@@ -145,22 +145,29 @@ mlx5_rx_mprq_replenish_bulk_mbuf(struct mlx5_rxq_data *rxq)
 	const uint32_t strd_n = 1 << rxq->strd_num_n;
 	const uint32_t elts_n = wqe_n * strd_n;
 	const uint32_t wqe_mask = elts_n - 1;
-	uint32_t n = rxq->elts_ci - rxq->rq_pi;
+	uint32_t n = elts_n - (rxq->elts_ci - rxq->rq_pi);
 	uint32_t elts_idx = rxq->elts_ci & wqe_mask;
 	struct rte_mbuf **elts = &(*rxq->elts)[elts_idx];
+	unsigned int i;
 
-	if (n <= rxq->rq_repl_thresh) {
-		MLX5_ASSERT(n + MLX5_VPMD_RX_MAX_BURST >=
-			    MLX5_VPMD_RXQ_RPLNSH_THRESH(elts_n));
+	if (n >= rxq->rq_repl_thresh &&
+	    rxq->elts_ci - rxq->rq_pi <= rxq->rq_repl_thresh) {
+		MLX5_ASSERT(n >= MLX5_VPMD_RXQ_RPLNSH_THRESH(elts_n));
 		MLX5_ASSERT(MLX5_VPMD_RXQ_RPLNSH_THRESH(elts_n) >
 			     MLX5_VPMD_DESCS_PER_LOOP);
 		/* Not to cross queue end. */
-		n = RTE_MIN(n + MLX5_VPMD_RX_MAX_BURST, elts_n - elts_idx);
+		n = RTE_MIN(n - MLX5_VPMD_DESCS_PER_LOOP, elts_n - elts_idx);
+		/* Limit replenish number to threshold value. */
+		n = RTE_MIN(n, rxq->rq_repl_thresh);
 		if (rte_mempool_get_bulk(rxq->mp, (void *)elts, n) < 0) {
 			rxq->stats.rx_nombuf += n;
 			return;
 		}
 		rxq->elts_ci += n;
+		/* Prevent overflowing into consumed mbufs. */
+		elts_idx = rxq->elts_ci & wqe_mask;
+		for (i = 0; i < MLX5_VPMD_DESCS_PER_LOOP; ++i)
+			(*rxq->elts)[elts_idx + i] = &rxq->fake_mbuf;
 	}
 }
 
-- 
2.24.1