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net: optimize skb_postpull_rcsum()

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Remove one pair of add/adc instructions and their dependency
against carry flag.

We can leverage third argument to csum_partial():

  X = csum_block_sub(X, csum_partial(start, len, 0), 0);

  -->

  X = csum_block_add(X, ~csum_partial(start, len, 0), 0);

  -->

  X = ~csum_partial(start, len, ~X);

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Eric Dumazet 2021-11-24 12:24:46 -08:00 committed by Jakub Kicinski
parent 0bd28476f6
commit 29c3002644
1 changed files with 5 additions and 1 deletions
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6
include/linux/skbuff.h
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@ -3485,7 +3485,11 @@ __skb_postpull_rcsum(struct sk_buff *skb, const void *start, unsigned int len,
static inline void skb_postpull_rcsum(struct sk_buff *skb,
const void *start, unsigned int len)
{
__skb_postpull_rcsum(skb, start, len, 0);
if (skb->ip_summed == CHECKSUM_COMPLETE)
skb->csum = ~csum_partial(start, len, ~skb->csum);
else if (skb->ip_summed == CHECKSUM_PARTIAL &&
skb_checksum_start_offset(skb) < 0)
skb->ip_summed = CHECKSUM_NONE;
}
static __always_inline void