Re: [PATCH net-next] ixgbe: flush when in xmit_more mode and under descriptor pressure

When xmit_more mode is being used and the ring is about to become
full, enforce a tail pointer write to the hw. Otherwise, we could
risk a Tx hang as pointed out by Alex.

Suggested-by: Alexander Duyck <redacted>
Signed-off-by: Daniel Borkmann <redacted>
---
 Hi Alex, something along that lines regarding your first comment?

 drivers/net/ethernet/intel/ixgbe/ixgbe_main.c | 67 +++++++++++++++------------
 1 file changed, 38 insertions(+), 29 deletions(-)

diff --git a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
index ba9ceaa..f851e84 100644
--- a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
+++ b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c

@@ -6853,6 +6883,7 @@ static void ixgbe_tx_map(struct ixgbe_ring *tx_ring,
 	u32 tx_flags = first->tx_flags;
 	u32 cmd_type = ixgbe_tx_cmd_type(skb, tx_flags);
 	u16 i = tx_ring->next_to_use;
+	bool desc_pressure;
 
 	tx_desc = IXGBE_TX_DESC(tx_ring, i);
 

@@ -6958,10 +6989,15 @@ static void ixgbe_tx_map(struct ixgbe_ring *tx_ring,
 
 	tx_ring->next_to_use = i;
 
-	if (!skb->xmit_more) {
+	desc_pressure = (ixgbe_desc_unused(tx_ring) < DESC_NEEDED);
+	if (!skb->xmit_more || unlikely(desc_pressure)) {
 		/* notify HW of packet */
 		ixgbe_write_tail(tx_ring, i);
+
+		if (unlikely(desc_pressure))
+			__ixgbe_maybe_stop_tx(tx_ring, DESC_NEEDED);
 	}
+
 	return;
 dma_error:
 	dev_err(tx_ring->dev, "TX DMA map failed\n");

@@ -6978,6 +7014,7 @@ dma_error:
 	}
 
 	tx_ring->next_to_use = i;
+	ixgbe_maybe_stop_tx(tx_ring, DESC_NEEDED);
 }