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skb: Drop bad code from pskb_expand_head 

The fast-path for pskb_expand_head contains a check where the size plus the
unaligned size of skb_shared_info is compared against the size of the data
buffer.  This code path has two issues.  First is the fact that after the
recent changes by Eric Dumazet to __alloc_skb and build_skb the shared info
is always placed in the optimal spot for a buffer size making this check
unnecessary.  The second issue is the fact that the check doesn't take into
account the aligned size of shared info.  As a result the code burns cycles
doing a memcpy with nothing actually being shifted.

Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Alexander Duyck 2012-05-04 14:26:46 +00:00 committed by David S. Miller
parent bd14b1b2e2
commit 9202e31d46
1 changed files with 0 additions and 12 deletions
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12
net/core/skbuff.c
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@ -951,17 +951,6 @@ int pskb_expand_head(struct sk_buff *skb, int nhead, int ntail,
fastpath = atomic_read(&skb_shinfo(skb)->dataref) == delta;
}
if (fastpath && !skb->head_frag &&
size + sizeof(struct skb_shared_info) <= ksize(skb->head)) {
memmove(skb->head + size, skb_shinfo(skb),
offsetof(struct skb_shared_info,
frags[skb_shinfo(skb)->nr_frags]));
memmove(skb->head + nhead, skb->head,
skb_tail_pointer(skb) - skb->head);
off = nhead;
goto adjust_others;
}
data = kmalloc(size + SKB_DATA_ALIGN(sizeof(struct skb_shared_info)),
gfp_mask);
if (!data)
@ -997,7 +986,6 @@ int pskb_expand_head(struct sk_buff *skb, int nhead, int ntail,
skb->head = data;
skb->head_frag = 0;
adjust_others:
skb->data += off;
#ifdef NET_SKBUFF_DATA_USES_OFFSET
skb->end = size;