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Commit 5804283d authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller
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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: default avatarEric Dumazet <edumazet@google.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent a8404ce5

drivers/net/ethernet/mellanox/mlx4/en_tx.c

+16 −7
Original line number Diff line number Diff line
@@ -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;