Commit 0bd28476 authored by Eric Dumazet's avatar Eric Dumazet Committed by Jakub Kicinski
Browse files

gro: optimize skb_gro_postpull_rcsum() 



We can leverage third argument to csum_partial():

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

  -->

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

  -->

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

This removes one add/adc pair and its dependency against the carry flag.

Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Signed-off-by: default avatarJakub Kicinski <kuba@kernel.org>
parent 70331909

include/net/gro.h

+2 −2
Original line number Diff line number Diff line
@@ -173,8 +173,8 @@ static inline void skb_gro_postpull_rcsum(struct sk_buff *skb, 
					const void *start, unsigned int len)

{

	if (NAPI_GRO_CB(skb)->csum_valid)

		NAPI_GRO_CB(skb)->csum = csum_sub(NAPI_GRO_CB(skb)->csum,

						  csum_partial(start, len, 0));

		NAPI_GRO_CB(skb)->csum = ~csum_partial(start, len,

						       ~NAPI_GRO_CB(skb)->csum);

}



/* GRO checksum functions. These are logical equivalents of the normal