On Thu, 29 Aug 2019 11:27:16 -0700, Shannon Nelson wrote:

+netdev_tx_t ionic_start_xmit(struct sk_buff *skb, struct net_device *netdev)
+{
+	u16 queue_index = skb_get_queue_mapping(skb);
+	struct ionic_lif *lif = netdev_priv(netdev);
+	struct ionic_queue *q;
+	int ndescs;
+	int err;
+
+	if (unlikely(!test_bit(IONIC_LIF_UP, lif->state))) {
+		dev_kfree_skb(skb);
+		return NETDEV_TX_OK;
+	}
+
+	if (likely(lif_to_txqcq(lif, queue_index)))
+		q = lif_to_txq(lif, queue_index);
+	else
+		q = lif_to_txq(lif, 0);
+
+	ndescs = ionic_tx_descs_needed(q, skb);
+	if (ndescs < 0)
+		goto err_out_drop;
+
+	if (!ionic_q_has_space(q, ndescs)) {

You should stop the queue in advance, whenever you can't ensure that a
max size frame can be placed on the ring. Requeuing is very expensive
so modern drivers should try to never return NETDEV_TX_BUSY

+		netif_stop_subqueue(netdev, queue_index);
+		q->stop++;
+
+		/* Might race with ionic_tx_clean, check again */
+		smp_rmb();
+		if (ionic_q_has_space(q, ndescs)) {
+			netif_wake_subqueue(netdev, queue_index);
+			q->wake++;
+		} else {
+			return NETDEV_TX_BUSY;
+		}
+	}
+
+	if (skb_is_gso(skb))
+		err = ionic_tx_tso(q, skb);
+	else
+		err = ionic_tx(q, skb);
+
+	if (err)
+		goto err_out_drop;
+
+	return NETDEV_TX_OK;
+
+err_out_drop:
+	netif_stop_subqueue(netdev, queue_index);

This stopping of the queue is suspicious, if ionic_tx() fails there's
no guarantee the queue will ever be woken up, no?

+	q->stop++;
+	q->drop++;
+	dev_kfree_skb(skb);
+	return NETDEV_TX_OK;
+}