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Date: Sun, 5 Oct 2014 12:35:13 +0300
From: Amir Vadai <amirv@...lanox.com>
To: "David S. Miller" <davem@...emloft.net>,
Eric Dumazet <edumazet@...gle.com>
Cc: netdev@...r.kernel.org, Yevgeny Petrilin <yevgenyp@...lanox.com>,
Or Gerlitz <ogerlitz@...lanox.com>,
Ido Shamay <idos@...lanox.com>, Amir Vadai <amirv@...lanox.com>
Subject: [PATCH net-next 05/14] net/mlx4_en: Avoid a cache line miss in TX completion for single frag skb's
From: Eric Dumazet <edumazet@...gle.com>
Add frag0_dma/frag0_byte_count into mlx4_en_tx_info to avoid a cache
line miss in TX completion for frames having one dma element. (We avoid
reading back the tx descriptor)
Note this could be extended to 2/3 dma elements later, as we have free
room in mlx4_en_tx_info
Also, mlx4_en_free_tx_desc() no longer accesses skb_shinfo(). We use a
new nr_maps fields in mlx4_en_tx_info to avoid 2 or 3 cache misses.
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Signed-off-by: Amir Vadai <amirv@...lanox.com>
---
drivers/net/ethernet/mellanox/mlx4/en_tx.c | 83 +++++++++++++++-------------
drivers/net/ethernet/mellanox/mlx4/mlx4_en.h | 3 +
2 files changed, 49 insertions(+), 37 deletions(-)
diff --git a/drivers/net/ethernet/mellanox/mlx4/en_tx.c b/drivers/net/ethernet/mellanox/mlx4/en_tx.c
index 1447906..edc4a88 100644
--- a/drivers/net/ethernet/mellanox/mlx4/en_tx.c
+++ b/drivers/net/ethernet/mellanox/mlx4/en_tx.c
@@ -259,38 +259,40 @@ static u32 mlx4_en_free_tx_desc(struct mlx4_en_priv *priv,
struct mlx4_en_tx_ring *ring,
int index, u8 owner, u64 timestamp)
{
- struct mlx4_en_dev *mdev = priv->mdev;
struct mlx4_en_tx_info *tx_info = &ring->tx_info[index];
struct mlx4_en_tx_desc *tx_desc = ring->buf + index * TXBB_SIZE;
struct mlx4_wqe_data_seg *data = (void *) tx_desc + tx_info->data_offset;
- struct sk_buff *skb = tx_info->skb;
- struct skb_frag_struct *frag;
void *end = ring->buf + ring->buf_size;
- int frags = skb_shinfo(skb)->nr_frags;
+ struct sk_buff *skb = tx_info->skb;
+ int nr_maps = tx_info->nr_maps;
int i;
- struct skb_shared_hwtstamps hwts;
- if (timestamp) {
- mlx4_en_fill_hwtstamps(mdev, &hwts, timestamp);
+ if (unlikely(timestamp)) {
+ struct skb_shared_hwtstamps hwts;
+
+ mlx4_en_fill_hwtstamps(priv->mdev, &hwts, timestamp);
skb_tstamp_tx(skb, &hwts);
}
/* Optimize the common case when there are no wraparounds */
if (likely((void *) tx_desc + tx_info->nr_txbb * TXBB_SIZE <= end)) {
if (!tx_info->inl) {
- if (tx_info->linear) {
+ if (tx_info->linear)
dma_unmap_single(priv->ddev,
- (dma_addr_t) be64_to_cpu(data->addr),
- be32_to_cpu(data->byte_count),
- PCI_DMA_TODEVICE);
- ++data;
- }
-
- for (i = 0; i < frags; i++) {
- frag = &skb_shinfo(skb)->frags[i];
+ tx_info->map0_dma,
+ tx_info->map0_byte_count,
+ PCI_DMA_TODEVICE);
+ else
+ dma_unmap_page(priv->ddev,
+ tx_info->map0_dma,
+ tx_info->map0_byte_count,
+ PCI_DMA_TODEVICE);
+ for (i = 1; i < nr_maps; i++) {
+ data++;
dma_unmap_page(priv->ddev,
- (dma_addr_t) be64_to_cpu(data[i].addr),
- skb_frag_size(frag), PCI_DMA_TODEVICE);
+ (dma_addr_t)be64_to_cpu(data->addr),
+ be32_to_cpu(data->byte_count),
+ PCI_DMA_TODEVICE);
}
}
} else {
@@ -299,23 +301,25 @@ static u32 mlx4_en_free_tx_desc(struct mlx4_en_priv *priv,
data = ring->buf + ((void *)data - end);
}
- if (tx_info->linear) {
+ if (tx_info->linear)
dma_unmap_single(priv->ddev,
- (dma_addr_t) be64_to_cpu(data->addr),
- be32_to_cpu(data->byte_count),
- PCI_DMA_TODEVICE);
- ++data;
- }
-
- for (i = 0; i < frags; i++) {
+ tx_info->map0_dma,
+ tx_info->map0_byte_count,
+ PCI_DMA_TODEVICE);
+ else
+ dma_unmap_page(priv->ddev,
+ tx_info->map0_dma,
+ tx_info->map0_byte_count,
+ PCI_DMA_TODEVICE);
+ for (i = 1; i < nr_maps; i++) {
+ data++;
/* Check for wraparound before unmapping */
if ((void *) data >= end)
data = ring->buf;
- frag = &skb_shinfo(skb)->frags[i];
dma_unmap_page(priv->ddev,
- (dma_addr_t) be64_to_cpu(data->addr),
- skb_frag_size(frag), PCI_DMA_TODEVICE);
- ++data;
+ (dma_addr_t)be64_to_cpu(data->addr),
+ be32_to_cpu(data->byte_count),
+ PCI_DMA_TODEVICE);
}
}
}
@@ -751,19 +755,22 @@ netdev_tx_t mlx4_en_xmit(struct sk_buff *skb, struct net_device *dev)
tx_info->linear = (lso_header_size < skb_headlen(skb) &&
!is_inline(ring->inline_thold, skb, NULL)) ? 1 : 0;
- data += skb_shinfo(skb)->nr_frags + tx_info->linear - 1;
+ tx_info->nr_maps = skb_shinfo(skb)->nr_frags + tx_info->linear;
+ data += tx_info->nr_maps - 1;
if (is_inline(ring->inline_thold, skb, &fragptr)) {
tx_info->inl = 1;
} else {
+ dma_addr_t dma = 0;
+ u32 byte_count = 0;
+
/* Map fragments if any */
for (i = skb_shinfo(skb)->nr_frags - 1; i >= 0; i--) {
const struct skb_frag_struct *frag;
- dma_addr_t dma;
-
frag = &skb_shinfo(skb)->frags[i];
+ byte_count = skb_frag_size(frag);
dma = skb_frag_dma_map(ddev, frag,
- 0, skb_frag_size(frag),
+ 0, byte_count,
DMA_TO_DEVICE);
if (dma_mapping_error(ddev, dma))
goto tx_drop_unmap;
@@ -771,14 +778,13 @@ netdev_tx_t mlx4_en_xmit(struct sk_buff *skb, struct net_device *dev)
data->addr = cpu_to_be64(dma);
data->lkey = ring->mr_key;
wmb();
- data->byte_count = cpu_to_be32(skb_frag_size(frag));
+ data->byte_count = cpu_to_be32(byte_count);
--data;
}
/* Map linear part if needed */
if (tx_info->linear) {
- u32 byte_count = skb_headlen(skb) - lso_header_size;
- dma_addr_t dma;
+ byte_count = skb_headlen(skb) - lso_header_size;
dma = dma_map_single(ddev, skb->data +
lso_header_size, byte_count,
@@ -792,6 +798,9 @@ netdev_tx_t mlx4_en_xmit(struct sk_buff *skb, struct net_device *dev)
data->byte_count = cpu_to_be32(byte_count);
}
tx_info->inl = 0;
+ /* tx completion can avoid cache line miss for common cases */
+ tx_info->map0_dma = dma;
+ tx_info->map0_byte_count = byte_count;
}
/*
diff --git a/drivers/net/ethernet/mellanox/mlx4/mlx4_en.h b/drivers/net/ethernet/mellanox/mlx4/mlx4_en.h
index ab34461..a904030 100644
--- a/drivers/net/ethernet/mellanox/mlx4/mlx4_en.h
+++ b/drivers/net/ethernet/mellanox/mlx4/mlx4_en.h
@@ -216,12 +216,15 @@ enum cq_type {
struct mlx4_en_tx_info {
struct sk_buff *skb;
+ dma_addr_t map0_dma;
+ u32 map0_byte_count;
u32 nr_txbb;
u32 nr_bytes;
u8 linear;
u8 data_offset;
u8 inl;
u8 ts_requested;
+ u8 nr_maps;
} ____cacheline_aligned_in_smp;
--
1.8.3.4
--
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