diff options
| author | Eric Dumazet <edumazet@google.com> | 2014-10-05 12:35:15 +0300 |
|---|---|---|
| committer | David S. Miller <davem@davemloft.net> | 2014-10-06 01:04:15 -0400 |
| commit | fb1843ee72c7b2ed784bf88ad79c6ccc2f652499 (patch) | |
| tree | 139741643875150cd8cc289b92790b63dcd73f3c | |
| parent | 29d40c903247596c954446639116467eb6689bb7 (diff) | |
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 <edumazet@google.com>
Signed-off-by: Amir Vadai <amirv@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
| -rw-r--r-- | drivers/net/ethernet/mellanox/mlx4/en_tx.c | 22 |
1 files 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 b96627c4972..d9aaeb2d019 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); /* |