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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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5
drivers/net/igb/igb_main.c
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@@ -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,