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commit 042a53a9e437feaf2230dd2cadcecfae9c7bfe05
Author: Eric Dumazet <eric.dumazet@gmail.com>
Date: Fri Jun 5 04:04:16 2009 +0000
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>
Index: hurd-debian/libdde-linux26/contrib/include/linux/skbuff.h
===================================================================
--- hurd-debian.orig/libdde-linux26/contrib/include/linux/skbuff.h 2012-04-16 00:26:40.000000000 +0000
+++ hurd-debian/libdde-linux26/contrib/include/linux/skbuff.h 2012-04-16 00:34:56.000000000 +0000
@@ -142,6 +142,9 @@
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;
@@ -152,7 +155,7 @@
struct sk_buff *frag_list;
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
};
Index: hurd-debian/libdde-linux26/contrib/net/core/skb_dma_map.c
===================================================================
--- hurd-debian.orig/libdde-linux26/contrib/net/core/skb_dma_map.c 2012-04-16 00:26:40.000000000 +0000
+++ hurd-debian/libdde-linux26/contrib/net/core/skb_dma_map.c 2012-04-16 00:34:56.000000000 +0000
@@ -20,7 +20,7 @@
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 @@
fp->size, dir);
if (dma_mapping_error(dev, map))
goto unwind;
- sp->dma_maps[i + 1] = map;
+ sp->dma_maps[i] = map;
}
sp->num_dma_maps = i + 1;
@@ -38,10 +38,10 @@
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;
@@ -54,12 +54,12 @@
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);
}
}
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