i40e/i40evf: Detect and recover hung queue scenario

In VFs, there is a known issue which can cause writebacks
to not occur when interrupts are disabled and there are
less than 4 descriptors resulting in TX timeout. Timeout
can also occur due to lost interrupt.

The current implementation for detecting and recovering
from hung queues in the PF is problematic because it actually
actively encourages lost interrupts.  By triggering a SW
interrupt, interrupts are forced on.  If we are already in
napi_poll and an interrupt fires, napi_poll will not be
rescheduled and the interrupt is effectively lost; thereby
potentially *causing* hung queues.

This patch checks whether packets are being processed between
every watchdog cycle and determine potential hung queue and
fires triggers SW interrupt only for that particular queue.

Signed-off-by: Sudheer Mogilappagari <sudheer.mogilappagari@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

1 files changed, 54 insertions, 0 deletions

diff --git a/drivers/net/ethernet/intel/i40e/i40e_txrx.c b/drivers/net/ethernet/intel/i40e/i40e_txrx.c
index 40edb6e5e6f6..8d2275830a40 100644
--- a/drivers/net/ethernet/intel/i40e/i40e_txrx.c
+++ b/drivers/net/ethernet/intel/i40e/i40e_txrx.c
@@ -726,6 +726,59 @@ u32 i40e_get_tx_pending(struct i40e_ring *ring)
 	return 0;
 }
 
+/**
+ * i40e_detect_recover_hung - Function to detect and recover hung_queues
+ * @vsi:  pointer to vsi struct with tx queues
+ *
+ * VSI has netdev and netdev has TX queues. This function is to check each of
+ * those TX queues if they are hung, trigger recovery by issuing SW interrupt.
+ **/
+void i40e_detect_recover_hung(struct i40e_vsi *vsi)
+{
+	struct i40e_ring *tx_ring = NULL;
+	struct net_device *netdev;
+	unsigned int i;
+	int packets;
+
+	if (!vsi)
+		return;
+
+	if (test_bit(__I40E_VSI_DOWN, vsi->state))
+		return;
+
+	netdev = vsi->netdev;
+	if (!netdev)
+		return;
+
+	if (!netif_carrier_ok(netdev))
+		return;
+
+	for (i = 0; i < vsi->num_queue_pairs; i++) {
+		tx_ring = vsi->tx_rings[i];
+		if (tx_ring && tx_ring->desc) {
+			/* If packet counter has not changed the queue is
+			 * likely stalled, so force an interrupt for this
+			 * queue.
+			 *
+			 * prev_pkt_ctr would be negative if there was no
+			 * pending work.
+			 */
+			packets = tx_ring->stats.packets & INT_MAX;
+			if (tx_ring->tx_stats.prev_pkt_ctr == packets) {
+				i40e_force_wb(vsi, tx_ring->q_vector);
+				continue;
+			}
+
+			/* Memory barrier between read of packet count and call
+			 * to i40e_get_tx_pending()
+			 */
+			smp_rmb();
+			tx_ring->tx_stats.prev_pkt_ctr =
+			    i40e_get_tx_pending(tx_ring) ? packets : -1;
+		}
+	}
+}
+
 #define WB_STRIDE 4
 
 /**
@@ -1163,6 +1216,7 @@ int i40e_setup_tx_descriptors(struct i40e_ring *tx_ring)
 
 	tx_ring->next_to_use = 0;
 	tx_ring->next_to_clean = 0;
+	tx_ring->tx_stats.prev_pkt_ctr = -1;
 	return 0;
 
 err: