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mlx4: exploit skb->xmit_more to conditionally send doorbell 

skb->xmit_more tells us if another skb is coming next.

We need to send doorbell when : xmit_more is not set,
or txqueue is stopped (preventing next skb to come immediately)

Tested with a modified pktgen version, I got a 40% increase of
throughput.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet 2014-09-25 07:17:49 -07:00 committed by David S. Miller
parent a8404ce5ae
commit 5804283d7c
1 changed files with 16 additions and 7 deletions
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21
drivers/net/ethernet/mellanox/mlx4/en_tx.c
View File

@ -667,6 +667,7 @@ netdev_tx_t mlx4_en_xmit(struct sk_buff *skb, struct net_device *dev)
int lso_header_size;
void *fragptr;
bool bounce = false;
bool send_doorbell;
if (!priv->port_up)
goto tx_drop;
@ -878,12 +879,16 @@ netdev_tx_t mlx4_en_xmit(struct sk_buff *skb, struct net_device *dev)
skb_tx_timestamp(skb);
if (ring->bf_enabled && desc_size <= MAX_BF && !bounce && !vlan_tx_tag_present(skb)) {
send_doorbell = !skb->xmit_more || netif_xmit_stopped(ring->tx_queue);
if (ring->bf_enabled && desc_size <= MAX_BF && !bounce &&
!vlan_tx_tag_present(skb) && send_doorbell) {
tx_desc->ctrl.bf_qpn |= cpu_to_be32(ring->doorbell_qpn);
op_own |= htonl((bf_index & 0xffff) << 8);
/* Ensure new descirptor hits memory
* before setting ownership of this descriptor to HW */
/* Ensure new descriptor hits memory
* before setting ownership of this descriptor to HW
*/
wmb();
tx_desc->ctrl.owner_opcode = op_own;
@ -896,12 +901,16 @@ netdev_tx_t mlx4_en_xmit(struct sk_buff *skb, struct net_device *dev)
ring->bf.offset ^= ring->bf.buf_size;
} else {
/* Ensure new descirptor hits memory
* before setting ownership of this descriptor to HW */
/* Ensure new descriptor hits memory
* before setting ownership of this descriptor to HW
*/
wmb();
tx_desc->ctrl.owner_opcode = op_own;
if (send_doorbell) {
wmb();
iowrite32be(ring->doorbell_qpn, ring->bf.uar->map + MLX4_SEND_DOORBELL);
iowrite32be(ring->doorbell_qpn,
ring->bf.uar->map + MLX4_SEND_DOORBELL);
}
}
return NETDEV_TX_OK;