[dpdk-dev] [PATCH] vdpa/mlx5: fix completion queue polling

[Matan Azrad]

The CQ polling is done in order to notify the guest about new traffic
bursts and to release FW resources for the next bursts management.

When HW is faster than SW, it may be that all the FW resources are busy
in SW due to late polling.
In this case, due to wrong WQE counter masking, the fullness
calculation of the completions number is 0 while the queue is full.

Change the WQE counter masking to 16-bit wideness instead of the CQ
size mask as defined by the CQE format.

Fixes: c5f714e50b0e ("vdpa/mlx5: optimize completion queue poll")
Cc: stable at dpdk.org

Signed-off-by: Matan Azrad <matan at nvidia.com>
Acked-by: Xueming Li <xuemingl at nvidia.com>
---
 drivers/vdpa/mlx5/mlx5_vdpa_event.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/drivers/vdpa/mlx5/mlx5_vdpa_event.c b/drivers/vdpa/mlx5/mlx5_vdpa_event.c
index 5a2d4fb..2672935 100644
--- a/drivers/vdpa/mlx5/mlx5_vdpa_event.c
+++ b/drivers/vdpa/mlx5/mlx5_vdpa_event.c
@@ -172,7 +172,7 @@
 	cq->callfd = callfd;
 	/* Init CQ to ones to be in HW owner in the start. */
 	cq->cqes[0].op_own = MLX5_CQE_OWNER_MASK;
-	cq->cqes[0].wqe_counter = rte_cpu_to_be_16(cq_size - 1);
+	cq->cqes[0].wqe_counter = rte_cpu_to_be_16(UINT16_MAX);
 	/* First arming. */
 	mlx5_vdpa_cq_arm(priv, cq);
 	return 0;
@@ -187,7 +187,6 @@
 	struct mlx5_vdpa_event_qp *eqp =
 				container_of(cq, struct mlx5_vdpa_event_qp, cq);
 	const unsigned int cq_size = 1 << cq->log_desc_n;
-	const unsigned int cq_mask = cq_size - 1;
 	union {
 		struct {
 			uint16_t wqe_counter;
@@ -196,13 +195,13 @@
 		};
 		uint32_t word;
 	} last_word;
-	uint16_t next_wqe_counter = cq->cq_ci & cq_mask;
+	uint16_t next_wqe_counter = cq->cq_ci;
 	uint16_t cur_wqe_counter;
 	uint16_t comp;
 
 	last_word.word = rte_read32(&cq->cqes[0].wqe_counter);
 	cur_wqe_counter = rte_be_to_cpu_16(last_word.wqe_counter);
-	comp = (cur_wqe_counter + 1u - next_wqe_counter) & cq_mask;
+	comp = cur_wqe_counter + (uint16_t)1 - next_wqe_counter;
 	if (comp) {
 		cq->cq_ci += comp;
 		MLX5_ASSERT(!!(cq->cq_ci & cq_size) ==
-- 
1.8.3.1