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net/mlx4_en: mlx4_en_xmit() reads ring->cons once, and ahead of time to avoid stalls

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Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Amir Vadai <amirv@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet 2014-10-05 12:35:16 +03:00 committed by David S. Miller
parent fb1843ee72
commit f905c79e12
1 changed files with 11 additions and 5 deletions
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16
drivers/net/ethernet/mellanox/mlx4/en_tx.c
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@ -691,10 +691,17 @@ netdev_tx_t mlx4_en_xmit(struct sk_buff *skb, struct net_device *dev)
void *fragptr;
bool bounce = false;
bool send_doorbell;
u32 ring_cons;
if (!priv->port_up)
goto tx_drop;
tx_ind = skb_get_queue_mapping(skb);
ring = priv->tx_ring[tx_ind];
/* fetch ring->cons far ahead before needing it to avoid stall */
ring_cons = ACCESS_ONCE(ring->cons);
real_size = get_real_size(skb, dev, &lso_header_size);
if (unlikely(!real_size))
goto tx_drop;
@ -708,13 +715,11 @@ netdev_tx_t mlx4_en_xmit(struct sk_buff *skb, struct net_device *dev)
goto tx_drop;
}
tx_ind = skb->queue_mapping;
ring = priv->tx_ring[tx_ind];
if (vlan_tx_tag_present(skb))
vlan_tag = vlan_tx_tag_get(skb);
/* Check available TXBBs And 2K spare for prefetch */
if (unlikely(((int)(ring->prod - ring->cons)) >
if (unlikely(((int)(ring->prod - ring_cons)) >
ring->size - HEADROOM - MAX_DESC_TXBBS)) {
/* every full Tx ring stops queue */
netif_tx_stop_queue(ring->tx_queue);
@ -728,7 +733,8 @@ netdev_tx_t mlx4_en_xmit(struct sk_buff *skb, struct net_device *dev)
*/
wmb();
if (unlikely(((int)(ring->prod - ring->cons)) <=
ring_cons = ACCESS_ONCE(ring->cons);
if (unlikely(((int)(ring->prod - ring_cons)) <=
ring->size - HEADROOM - MAX_DESC_TXBBS)) {
netif_tx_wake_queue(ring->tx_queue);
ring->wake_queue++;
@ -741,7 +747,7 @@ netdev_tx_t mlx4_en_xmit(struct sk_buff *skb, struct net_device *dev)
/* Track current inflight packets for performance analysis */
AVG_PERF_COUNTER(priv->pstats.inflight_avg,
(u32) (ring->prod - ring->cons - 1));
(u32)(ring->prod - ring_cons - 1));
/* Packet is good - grab an index and transmit it */
index = ring->prod & ring->size_mask;