[dpdk-dev] [PATCH v1] net/mlx5: return EAGAIN on premature disable interrupt calls

[Ophir Munk <ophirmu@mellanox.com>]

RXQ interrupts under Linux are based on the epoll mechanism. An
expected order of operations is as follows:
1. Call rte_eth_dev_rx_intr_enable(), to arm the CQ for receiving events
on data input.
2. Block on rte_epoll_wait() with an array of file descriptors
representing the CQ events. Upon data arrival the kernel will signal an
input event on the corresponding CQ fd.
3. Call rte_eth_dev_rx_intr_disable() after the event was received and
continue in polling mode. The mlx5 implementation of
rte_eth_dev_rx_intr_disable() is to get the CQ event and ack it.

In practice applications may wake up from rte_epoll_wait() due to
timeout with no event to ack but still call
rte_eth_dev_rx_intr_disable() unconditionally.  In such cases the call
should return EAGAIN (since the file descriptors are non-blocked), as
opposed to EINVAL which indicates a real failure.  In case of EAGAIN the
PMD should not warn on "Unable to disable interrupt on Rx queue".

Signed-off-by: Ophir Munk <ophirmu@mellanox.com>
Acked-by: Viacheslav Ovsiienko <viacheslavo@mellanox.com>
---
 drivers/net/mlx5/mlx5_rxq.c | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/drivers/net/mlx5/mlx5_rxq.c b/drivers/net/mlx5/mlx5_rxq.c
index b436f06..38dfb98 100644
--- a/drivers/net/mlx5/mlx5_rxq.c
+++ b/drivers/net/mlx5/mlx5_rxq.c
@@ -936,7 +936,14 @@ mlx5_rx_intr_disable(struct rte_eth_dev *dev, uint16_t rx_queue_id)
 	}
 	ret = mlx5_glue->get_cq_event(rxq_obj->channel, &ev_cq, &ev_ctx);
 	if (ret || ev_cq != rxq_obj->cq) {
-		rte_errno = EINVAL;
+		/**
+		 * For non-zero 'ret' - save the errno (may be EAGAIN which
+		 * means this function was called before receiving an event).
+		 */
+		if (ret)
+			rte_errno = errno;
+		else
+			rte_errno = EINVAL;
 		goto exit;
 	}
 	rxq_data->cq_arm_sn++;
@@ -947,8 +954,9 @@ mlx5_rx_intr_disable(struct rte_eth_dev *dev, uint16_t rx_queue_id)
 	ret = rte_errno; /* Save rte_errno before cleanup. */
 	if (rxq_obj)
 		mlx5_rxq_obj_release(rxq_obj);
-	DRV_LOG(WARNING, "port %u unable to disable interrupt on Rx queue %d",
-		dev->data->port_id, rx_queue_id);
+	if (ret != EAGAIN)
+		DRV_LOG(WARNING, "port %u unable to disable interrupt on Rx queue %d",
+			dev->data->port_id, rx_queue_id);
 	rte_errno = ret; /* Restore rte_errno. */
 	return -rte_errno;
 }
-- 
2.8.4