From fb1843ee72c7b2ed784bf88ad79c6ccc2f652499 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Sun, 5 Oct 2014 12:35:15 +0300 Subject: [PATCH] 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: Eric Dumazet Signed-off-by: Amir Vadai Signed-off-by: David S. Miller --- drivers/net/ethernet/mellanox/mlx4/en_tx.c | 22 +++++++++++++++------- 1 file changed, 15 insertions(+), 7 deletions(-) diff --git a/drivers/net/ethernet/mellanox/mlx4/en_tx.c b/drivers/net/ethernet/mellanox/mlx4/en_tx.c index b96627c4972f..d9aaeb2d019f 100644 --- a/drivers/net/ethernet/mellanox/mlx4/en_tx.c +++ b/drivers/net/ethernet/mellanox/mlx4/en_tx.c @@ -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); /* -- 2.20.1