net/mlx5: DR, select MSIX vector 0 for completion queue creation

When creating a software steering completion queue (CQ), an arbitrary
MSIX vector n is selected. This results in the CQ sharing the same
Ethernet traffic channel n associated with the chosen vector. However,
the value of n is often unpredictable, which can introduce complications
for interrupt monitoring and verification tools.

Moreover, SW steering uses polling rather than event-driven interrupts.
Therefore, there is no need to select any MSIX vector other than the
existing vector 0 for CQ creation.

In light of these factors, and to enhance predictability, we modify the
code to consistently select MSIX vector 0 for CQ creation.

Fixes: 297ccce ("net/mlx5: DR, Expose an internal API to issue RDMA operations")
Signed-off-by: Shahar Shitrit <[email protected]>
Reviewed-by: Yevgeny Kliteynik <[email protected]>
Signed-off-by: Tariq Toukan <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Jakub Kicinski <[email protected]>

Author: Shahar Shitrit

drivers/net/ethernet/mellanox/mlx5/core/steering/sws/dr_send.c

@@ -1067,7 +1067,6 @@ static struct mlx5dr_cq *dr_create_cq(struct mlx5_core_dev *mdev,
 	int inlen, err, eqn;
 	void *cqc, *in;
 	__be64 *pas;
-	int vector;
 	u32 i;
 
 	cq = kzalloc(sizeof(*cq), GFP_KERNEL);
@@ -1096,8 +1095,7 @@ static struct mlx5dr_cq *dr_create_cq(struct mlx5_core_dev *mdev,
 	if (!in)
 		goto err_cqwq;
 
-	vector = raw_smp_processor_id() % mlx5_comp_vectors_max(mdev);
-	err = mlx5_comp_eqn_get(mdev, vector, &eqn);
+	err = mlx5_comp_eqn_get(mdev, 0, &eqn);
 	if (err) {
 		kvfree(in);
 		goto err_cqwq;