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Message-ID: <CANn89i+HmN3DbfAtH+Uq_pBWYHXp5ioH8LyhGRAiHZhRLbs1nw@mail.gmail.com>
Date: Thu, 25 Nov 2021 05:32:23 -0800
From: Eric Dumazet <edumazet@...gle.com>
To: David Laight <David.Laight@...lab.com>
Cc: Eric Dumazet <eric.dumazet@...il.com>,
"David S . Miller" <davem@...emloft.net>,
Jakub Kicinski <kuba@...nel.org>,
netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next 2/2] net: optimize skb_postpull_rcsum()
On Thu, Nov 25, 2021 at 1:41 AM David Laight <David.Laight@...lab.com> wrote:
>
> From: Eric Dumazet
> > Sent: 24 November 2021 20:25
> >
> > From: Eric Dumazet <edumazet@...gle.com>
> >
> > 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);
>
> That doesn't seem to refer to the change in this file.
>
It is describing the change.
The first step, of copying first the __skb_postpull_rcsum(skb, start,
len, 0) content
into __skb_postpull_rcsum() was kind of obvious.
> David
>
> >
> > Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> > ---
> > include/linux/skbuff.h | 6 +++++-
> > 1 file changed, 5 insertions(+), 1 deletion(-)
> >
> > diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
> > index eba256af64a577b458998845f2dc01a5ec80745a..eae4bd3237a41cc1b60b44c91fbfe21dfdd8f117 100644
> > --- a/include/linux/skbuff.h
> > +++ b/include/linux/skbuff.h
> > @@ -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
> > --
> > 2.34.0.rc2.393.gf8c9666880-goog
>
> -
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