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>

1 files changed, 2 insertions, 2 deletions

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;