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skbuff: micro-optimize {,__}skb_header_pointer()

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{,__}skb_header_pointer() helpers exist mainly for preventing
accesses-beyond-end of the linear data.
In the vast majorify of cases, they bail out on the first condition.
All code going after is mostly a fallback.
Mark the most common branch as 'likely' one to move it in-line.
Also, skb_copy_bits() can return negative values only when the input
arguments are invalid, e.g. offset is greater than skb->len. It can
be safely marked as 'unlikely' branch, assuming that hotpath code
provides sane input to not fail here.

These two bump the throughput with a single Flow Dissector pass on
every packet (e.g. with RPS or driver that uses eth_get_headlen())
on 20 Mbps per flow/core.

Signed-off-by: Alexander Lobakin <alobakin@pm.me>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Alexander Lobakin 2021-03-14 11:11:50 +00:00 committed by David S. Miller
parent 59753ce8b1
commit d206121faf
1 changed files with 2 additions and 3 deletions
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5
include/linux/skbuff.h
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@ -3680,11 +3680,10 @@ static inline void * __must_check
__skb_header_pointer(const struct sk_buff *skb, int offset, int len,
const void *data, int hlen, void *buffer)
{
if (hlen - offset >= len)
if (likely(hlen - offset >= len))
return (void *)data + offset;
if (!skb ||
skb_copy_bits(skb, offset, buffer, len) < 0)
if (!skb || unlikely(skb_copy_bits(skb, offset, buffer, len) < 0))
return NULL;
return buffer;