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gro: optimize skb_gro_postpull_rcsum()

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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: Eric Dumazet <edumazet@google.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Eric Dumazet 2021-11-24 12:24:45 -08:00 committed by Jakub Kicinski
parent 703319094c
commit 0bd28476f6
1 changed files with 2 additions and 2 deletions
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4
include/net/gro.h
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@ -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