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Commit fb1843ee authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller
Browse files

net/mlx4_en: Avoid false sharing in mlx4_en_en_process_tx_cq() 



mlx4_en_process_tx_cq() carefully fetches and writes ring->last_nr_txbb
and ring->cons only one time to avoid false sharing

Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Signed-off-by: default avatarAmir Vadai <amirv@mellanox.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 29d40c90

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

+15 −7
Original line number Diff line number Diff line
@@ -387,6 +387,8 @@ static bool mlx4_en_process_tx_cq(struct net_device *dev, 
	u64 timestamp = 0;

	int done = 0;

	int budget = priv->tx_work_limit;

	u32 last_nr_txbb;

	u32 ring_cons;



	if (!priv->port_up)

		return true;
@@ -394,7 +396,9 @@ static bool mlx4_en_process_tx_cq(struct net_device *dev, 
	prefetchw(&ring->tx_queue->dql.limit);

	index = cons_index & size_mask;

	cqe = mlx4_en_get_cqe(buf, index, priv->cqe_size) + factor;

	ring_index = ring->cons & size_mask;

	last_nr_txbb = ACCESS_ONCE(ring->last_nr_txbb);

	ring_cons = ACCESS_ONCE(ring->cons);

	ring_index = ring_cons & size_mask;

	stamp_index = ring_index;



	/* Process all completed CQEs */
@@ -419,19 +423,19 @@ static bool mlx4_en_process_tx_cq(struct net_device *dev, 
		new_index = be16_to_cpu(cqe->wqe_index) & size_mask;



		do {

			txbbs_skipped += ring->last_nr_txbb;

			ring_index = (ring_index + ring->last_nr_txbb) & size_mask;

			txbbs_skipped += last_nr_txbb;

			ring_index = (ring_index + last_nr_txbb) & size_mask;

			if (ring->tx_info[ring_index].ts_requested)

				timestamp = mlx4_en_get_cqe_ts(cqe);



			/* free next descriptor */

			ring->last_nr_txbb = mlx4_en_free_tx_desc(

			last_nr_txbb = mlx4_en_free_tx_desc(

					priv, ring, ring_index,

					!!((ring->cons + txbbs_skipped) &

					!!((ring_cons + txbbs_skipped) &

					ring->size), timestamp);



			mlx4_en_stamp_wqe(priv, ring, stamp_index,

					  !!((ring->cons + txbbs_stamp) &

					  !!((ring_cons + txbbs_stamp) &

						ring->size));

			stamp_index = ring_index;

			txbbs_stamp = txbbs_skipped;
@@ -452,7 +456,11 @@ static bool mlx4_en_process_tx_cq(struct net_device *dev, 
	mcq->cons_index = cons_index;

	mlx4_cq_set_ci(mcq);

	wmb();

	ring->cons += txbbs_skipped;



	/* we want to dirty this cache line once */

	ACCESS_ONCE(ring->last_nr_txbb) = last_nr_txbb;

	ACCESS_ONCE(ring->cons) = ring_cons + txbbs_skipped;



	netdev_tx_completed_queue(ring->tx_queue, packets, bytes);



	/*