From 3d03641cb4ea050f969dd3ab34113adb95287f36 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Sun, 5 Oct 2014 12:35:13 +0300 Subject: [PATCH] net/mlx4_en: Avoid a cache line miss in TX completion for single frag skb's 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 Signed-off-by: Amir Vadai Signed-off-by: David S. Miller --- 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 14479068001f..edc4a8810368 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, - (dma_addr_t) be64_to_cpu(data[i].addr), - skb_frag_size(frag), PCI_DMA_TODEVICE); + 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->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 ab34461e628c..a90403000577 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;