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net: skb_shared_info optimization

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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>
This commit is contained in:
Eric Dumazet
2009-06-05 04:04:16 +00:00
committed by David S. Miller
parent eae3f29cc7
commit 042a53a9e4
10 changed files with 30 additions and 29 deletions
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4
drivers/net/ixgb/ixgb_main.c
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@@ -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;