net: skb_shared_info optimization

skb_dma_unmap() is quite expensive for small packets,
because we use two different cache lines from skb_shared_info.

One to access nr_frags, one to access dma_maps[0]

Instead of dma_maps being an array of MAX_SKB_FRAGS + 1 elements,
let dma_head alone in a new dma_head field, close to nr_frags,
to reduce cache lines misses.

Tested on my dev machine (bnx2 & tg3 adapters), nice speedup !

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

10 files changed, 30 insertions, 29 deletions

diff --git a/drivers/net/bnx2.c b/drivers/net/bnx2.c
index f53017250e09..391d2d47089c 100644
--- a/drivers/net/bnx2.c
+++ b/drivers/net/bnx2.c
@@ -5487,7 +5487,7 @@ bnx2_run_loopback(struct bnx2 *bp, int loopback_mode)
                 dev_kfree_skb(skb);
                 return -EIO;
         }
-        map = skb_shinfo(skb)->dma_maps[0];
+        map = skb_shinfo(skb)->dma_head;
 
         REG_WR(bp, BNX2_HC_COMMAND,
                bp->hc_cmd | BNX2_HC_COMMAND_COAL_NOW_WO_INT);
@@ -6167,7 +6167,7 @@ bnx2_start_xmit(struct sk_buff *skb, struct net_device *dev)
         }
 
         sp = skb_shinfo(skb);
-        mapping = sp->dma_maps[0];
+        mapping = sp->dma_head;
 
         tx_buf = &txr->tx_buf_ring[ring_prod];
         tx_buf->skb = skb;
@@ -6191,7 +6191,7 @@ bnx2_start_xmit(struct sk_buff *skb, struct net_device *dev)
                 txbd = &txr->tx_desc_ring[ring_prod];
 
                 len = frag->size;
-                mapping = sp->dma_maps[i + 1];
+                mapping = sp->dma_maps[i];
 
                 txbd->tx_bd_haddr_hi = (u64) mapping >> 32;
                 txbd->tx_bd_haddr_lo = (u64) mapping & 0xffffffff;
diff --git a/drivers/net/e1000/e1000_main.c b/drivers/net/e1000/e1000_main.c
index 05e87a59f1c6..8d36743c8140 100644
--- a/drivers/net/e1000/e1000_main.c
+++ b/drivers/net/e1000/e1000_main.c
@@ -2998,7 +2998,7 @@ static int e1000_tx_map(struct e1000_adapter *adapter,
                         size -= 4;
 
                 buffer_info->length = size;
-                buffer_info->dma = map[0] + offset;
+                buffer_info->dma = skb_shinfo(skb)->dma_head + offset;
                 buffer_info->time_stamp = jiffies;
                 buffer_info->next_to_watch = i;
 
@@ -3039,7 +3039,7 @@ static int e1000_tx_map(struct e1000_adapter *adapter,
                                 size -= 4;
 
                         buffer_info->length = size;
-                        buffer_info->dma = map[f + 1] + offset;
+                        buffer_info->dma = map[f] + offset;
                         buffer_info->time_stamp = jiffies;
                         buffer_info->next_to_watch = i;
 
diff --git a/drivers/net/e1000e/netdev.c b/drivers/net/e1000e/netdev.c
index 38694c79edcc..9043f1b845fe 100644
--- a/drivers/net/e1000e/netdev.c
+++ b/drivers/net/e1000e/netdev.c
@@ -3916,7 +3916,7 @@ static int e1000_tx_map(struct e1000_adapter *adapter,
                 buffer_info->length = size;
                 buffer_info->time_stamp = jiffies;
                 buffer_info->next_to_watch = i;
-                buffer_info->dma = map[0] + offset;
+                buffer_info->dma = skb_shinfo(skb)->dma_head + offset;
                 count++;
 
                 len -= size;
@@ -3947,7 +3947,7 @@ static int e1000_tx_map(struct e1000_adapter *adapter,
                         buffer_info->length = size;
                         buffer_info->time_stamp = jiffies;
                         buffer_info->next_to_watch = i;
-                        buffer_info->dma = map[f + 1] + offset;
+                        buffer_info->dma = map[f] + offset;
 
                         len -= size;
                         offset += size;
diff --git a/drivers/net/igb/igb_main.c b/drivers/net/igb/igb_main.c
index 958b2879da48..ea17319624aa 100644
--- a/drivers/net/igb/igb_main.c
+++ b/drivers/net/igb/igb_main.c
@@ -3139,8 +3139,7 @@ static inline int igb_tx_map_adv(struct igb_adapter *adapter,
         /* set time_stamp *before* dma to help avoid a possible race */
         buffer_info->time_stamp = jiffies;
         buffer_info->next_to_watch = i;
-        buffer_info->dma = map[count];
-        count++;
+        buffer_info->dma = skb_shinfo(skb)->dma_head;
 
         for (f = 0; f < skb_shinfo(skb)->nr_frags; f++) {
                 struct skb_frag_struct *frag;
@@ -3164,7 +3163,7 @@ static inline int igb_tx_map_adv(struct igb_adapter *adapter,
         tx_ring->buffer_info[i].skb = skb;
         tx_ring->buffer_info[first].next_to_watch = i;
 
-        return count;
+        return count + 1;
 }
 
 static inline void igb_tx_queue_adv(struct igb_adapter *adapter,
diff --git a/drivers/net/igbvf/netdev.c b/drivers/net/igbvf/netdev.c
index 5f7ba1a4990b..22aadb7884fa 100644
--- a/drivers/net/igbvf/netdev.c
+++ b/drivers/net/igbvf/netdev.c
@@ -2119,8 +2119,7 @@ static inline int igbvf_tx_map_adv(struct igbvf_adapter *adapter,
         /* set time_stamp *before* dma to help avoid a possible race */
         buffer_info->time_stamp = jiffies;
         buffer_info->next_to_watch = i;
-        buffer_info->dma = map[count];
-        count++;
+        buffer_info->dma = skb_shinfo(skb)->dma_head;
 
         for (f = 0; f < skb_shinfo(skb)->nr_frags; f++) {
                 struct skb_frag_struct *frag;
@@ -2144,7 +2143,7 @@ static inline int igbvf_tx_map_adv(struct igbvf_adapter *adapter,
         tx_ring->buffer_info[i].skb = skb;
         tx_ring->buffer_info[first].next_to_watch = i;
 
-        return count;
+        return count + 1;
 }
 
 static inline void igbvf_tx_queue_adv(struct igbvf_adapter *adapter,
diff --git a/drivers/net/ixgb/ixgb_main.c b/drivers/net/ixgb/ixgb_main.c
index 6eb7f37a113b..9c897cf86b9f 100644
--- a/drivers/net/ixgb/ixgb_main.c
+++ b/drivers/net/ixgb/ixgb_main.c
@@ -1300,7 +1300,7 @@ ixgb_tx_map(struct ixgb_adapter *adapter, struct sk_buff *skb,
                 buffer_info->length = size;
                 WARN_ON(buffer_info->dma != 0);
                 buffer_info->time_stamp = jiffies;
-                buffer_info->dma = map[0] + offset;
+                buffer_info->dma = skb_shinfo(skb)->dma_head + offset;
                         pci_map_single(adapter->pdev,
                                 skb->data + offset,
                                 size,
@@ -1340,7 +1340,7 @@ ixgb_tx_map(struct ixgb_adapter *adapter, struct sk_buff *skb,
 
                         buffer_info->length = size;
                         buffer_info->time_stamp = jiffies;
-                        buffer_info->dma = map[f + 1] + offset;
+                        buffer_info->dma = map[f] + offset;
                         buffer_info->next_to_watch = 0;
 
                         len -= size;
diff --git a/drivers/net/ixgbe/ixgbe_main.c b/drivers/net/ixgbe/ixgbe_main.c
index d36003cbb6d4..09994e920d5d 100644
--- a/drivers/net/ixgbe/ixgbe_main.c
+++ b/drivers/net/ixgbe/ixgbe_main.c
@@ -4837,7 +4837,7 @@ static int ixgbe_tx_map(struct ixgbe_adapter *adapter,
                 size = min(len, (uint)IXGBE_MAX_DATA_PER_TXD);
 
                 tx_buffer_info->length = size;
-                tx_buffer_info->dma = map[0] + offset;
+                tx_buffer_info->dma = skb_shinfo(skb)->dma_head + offset;
                 tx_buffer_info->time_stamp = jiffies;
                 tx_buffer_info->next_to_watch = i;
 
@@ -4869,7 +4869,7 @@ static int ixgbe_tx_map(struct ixgbe_adapter *adapter,
                         size = min(len, (uint)IXGBE_MAX_DATA_PER_TXD);
 
                         tx_buffer_info->length = size;
-                        tx_buffer_info->dma = map[f + 1] + offset;
+                        tx_buffer_info->dma = map[f] + offset;
                         tx_buffer_info->time_stamp = jiffies;
                         tx_buffer_info->next_to_watch = i;
 
diff --git a/drivers/net/tg3.c b/drivers/net/tg3.c
index a39b534fb43e..46a3f86125be 100644
--- a/drivers/net/tg3.c
+++ b/drivers/net/tg3.c
@@ -5021,7 +5021,7 @@ static int tigon3_dma_hwbug_workaround(struct tg3 *tp, struct sk_buff *skb,
                 /* New SKB is guaranteed to be linear. */
                 entry = *start;
                 ret = skb_dma_map(&tp->pdev->dev, new_skb, DMA_TO_DEVICE);
-                new_addr = skb_shinfo(new_skb)->dma_maps[0];
+                new_addr = skb_shinfo(new_skb)->dma_head;
 
                 /* Make sure new skb does not cross any 4G boundaries.
                  * Drop the packet if it does.
@@ -5155,7 +5155,7 @@ static int tg3_start_xmit(struct sk_buff *skb, struct net_device *dev)
 
         sp = skb_shinfo(skb);
 
-        mapping = sp->dma_maps[0];
+        mapping = sp->dma_head;
 
         tp->tx_buffers[entry].skb = skb;
 
@@ -5173,7 +5173,7 @@ static int tg3_start_xmit(struct sk_buff *skb, struct net_device *dev)
                         skb_frag_t *frag = &skb_shinfo(skb)->frags[i];
 
                         len = frag->size;
-                        mapping = sp->dma_maps[i + 1];
+                        mapping = sp->dma_maps[i];
                         tp->tx_buffers[entry].skb = NULL;
 
                         tg3_set_txd(tp, entry, mapping, len,
@@ -5331,7 +5331,7 @@ static int tg3_start_xmit_dma_bug(struct sk_buff *skb, struct net_device *dev)
 
         sp = skb_shinfo(skb);
 
-        mapping = sp->dma_maps[0];
+        mapping = sp->dma_head;
 
         tp->tx_buffers[entry].skb = skb;
 
@@ -5356,7 +5356,7 @@ static int tg3_start_xmit_dma_bug(struct sk_buff *skb, struct net_device *dev)
                         skb_frag_t *frag = &skb_shinfo(skb)->frags[i];
 
                         len = frag->size;
-                        mapping = sp->dma_maps[i + 1];
+                        mapping = sp->dma_maps[i];
 
                         tp->tx_buffers[entry].skb = NULL;
 
diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 7485058125e3..aad484cd5863 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -189,6 +189,9 @@ struct skb_shared_info {
         atomic_t        dataref;
         unsigned short  nr_frags;
         unsigned short  gso_size;
+#ifdef CONFIG_HAS_DMA
+        dma_addr_t      dma_head;
+#endif
         /* Warning: this field is not always filled in (UFO)! */
         unsigned short  gso_segs;
         unsigned short  gso_type;
@@ -198,7 +201,7 @@ struct skb_shared_info {
         struct skb_shared_hwtstamps hwtstamps;
         skb_frag_t      frags[MAX_SKB_FRAGS];
 #ifdef CONFIG_HAS_DMA
-        dma_addr_t      dma_maps[MAX_SKB_FRAGS + 1];
+        dma_addr_t      dma_maps[MAX_SKB_FRAGS];
 #endif
         /* Intermediate layers must ensure that destructor_arg
          * remains valid until skb destructor */
diff --git a/net/core/skb_dma_map.c b/net/core/skb_dma_map.c
index 7adb623ef664..79687dfd6957 100644
--- a/net/core/skb_dma_map.c
+++ b/net/core/skb_dma_map.c
@@ -20,7 +20,7 @@ int skb_dma_map(struct device *dev, struct sk_buff *skb,
         if (dma_mapping_error(dev, map))
                 goto out_err;
 
-        sp->dma_maps[0] = map;
+        sp->dma_head = map;
         for (i = 0; i < sp->nr_frags; i++) {
                 skb_frag_t *fp = &sp->frags[i];
 
@@ -28,7 +28,7 @@ int skb_dma_map(struct device *dev, struct sk_buff *skb,
                                    fp->size, dir);
                 if (dma_mapping_error(dev, map))
                         goto unwind;
-                sp->dma_maps[i + 1] = map;
+                sp->dma_maps[i] = map;
         }
 
         return 0;
@@ -37,10 +37,10 @@ unwind:
         while (--i >= 0) {
                 skb_frag_t *fp = &sp->frags[i];
 
-                dma_unmap_page(dev, sp->dma_maps[i + 1],
+                dma_unmap_page(dev, sp->dma_maps[i],
                                fp->size, dir);
         }
-        dma_unmap_single(dev, sp->dma_maps[0],
+        dma_unmap_single(dev, sp->dma_head,
                          skb_headlen(skb), dir);
 out_err:
         return -ENOMEM;
@@ -53,12 +53,12 @@ void skb_dma_unmap(struct device *dev, struct sk_buff *skb,
         struct skb_shared_info *sp = skb_shinfo(skb);
         int i;
 
-        dma_unmap_single(dev, sp->dma_maps[0],
+        dma_unmap_single(dev, sp->dma_head,
                          skb_headlen(skb), dir);
         for (i = 0; i < sp->nr_frags; i++) {
                 skb_frag_t *fp = &sp->frags[i];
 
-                dma_unmap_page(dev, sp->dma_maps[i + 1],
+                dma_unmap_page(dev, sp->dma_maps[i],
                                fp->size, dir);
         }
 }