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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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12
net/core/skb_dma_map.c
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@@ -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);
}
}