Commit 29c30026 authored by Eric Dumazet's avatar Eric Dumazet Committed by Jakub Kicinski
Browse files

net: optimize skb_postpull_rcsum() 



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: default avatarEric Dumazet <edumazet@google.com>
Signed-off-by: default avatarJakub Kicinski <kuba@kernel.org>
parent 0bd28476

include/linux/skbuff.h

+5 −1
Original line number Diff line number Diff line
@@ -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