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authorEric Dumazet <edumazet@google.com>2014-10-05 12:35:15 +0300
committerDavid S. Miller <davem@davemloft.net>2014-10-06 01:04:15 -0400
commitfb1843ee72c7b2ed784bf88ad79c6ccc2f652499 (patch)
tree139741643875150cd8cc289b92790b63dcd73f3c
parent29d40c903247596c954446639116467eb6689bb7 (diff)
downloadlinux-fb1843ee72c7b2ed784bf88ad79c6ccc2f652499.tar.bz2
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.c22
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 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);
/*