From: David Laight <David.Laight@ACULAB.COM>
To: 'Vladimir Oltean' <olteanv@gmail.com>,
Eric Dumazet <eric.dumazet@gmail.com>
Cc: "David S . Miller" <davem@davemloft.net>,
Jakub Kicinski <kuba@kernel.org>, netdev <netdev@vger.kernel.org>,
Eric Dumazet <edumazet@google.com>
Subject: RE: [PATCH net-next 2/2] net: optimize skb_postpull_rcsum()
Date: Thu, 2 Dec 2021 15:06:06 +0000 [thread overview]
Message-ID: <88b82ae31dc54a4c8b2173487f61ffe9@AcuMS.aculab.com> (raw)
In-Reply-To: <20211202131040.rdxzbfwh2slhftg5@skbuf>
From: Vladimir Oltean
> Sent: 02 December 2021 13:11
...
> > --- 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);
You can't do that, the domain is 1..0xffff (or maybe 0xffffffff).
The invert has to convert ~0 to ~0 not zero.
...
> There seems to be a disparity when the skb->csum is calculated by
> skb_postpull_rcsum as zero. Before, it was calculated as 0xffff.
Which is what that will do for some inputs at least.
Maybe:
skb->csum = 1 + ~csum_partial(start, len, ~skb->csum + 1);
is right.
I think that is the same as:
skb->csum = -csum_partial(start, len, -skb->csum);
Although letting the compiler do that transform probably makes
the code easier to read.
David
-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
next prev parent reply other threads:[~2021-12-02 15:06 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-11-24 20:24 [PATCH net-next 0/2] net: small csum optimizations Eric Dumazet
2021-11-24 20:24 ` [PATCH net-next 1/2] gro: optimize skb_gro_postpull_rcsum() Eric Dumazet
2021-11-24 20:24 ` [PATCH net-next 2/2] net: optimize skb_postpull_rcsum() Eric Dumazet
2021-11-25 9:41 ` David Laight
2021-11-25 13:32 ` Eric Dumazet
2021-11-25 14:29 ` David Laight
2021-12-02 13:10 ` Vladimir Oltean
2021-12-02 14:51 ` Eric Dumazet
2021-12-02 16:29 ` Vladimir Oltean
2021-12-02 19:32 ` Eric Dumazet
2021-12-02 20:37 ` Eric Dumazet
2021-12-02 21:07 ` Vladimir Oltean
2021-12-02 20:40 ` Vladimir Oltean
2021-12-02 20:58 ` Vladimir Oltean
2021-12-02 20:58 ` David Laight
2021-12-02 21:40 ` Vladimir Oltean
2021-12-03 14:51 ` David Laight
2021-12-03 14:57 ` David Laight
2021-12-03 16:14 ` Vladimir Oltean
2021-12-03 16:30 ` Eric Dumazet
2021-12-03 16:47 ` David Laight
2021-12-03 16:58 ` Eric Dumazet
2021-12-03 17:41 ` David Laight
2021-12-02 15:06 ` David Laight [this message]
2021-12-02 15:22 ` Eric Dumazet
2021-11-26 5:20 ` [PATCH net-next 0/2] net: small csum optimizations patchwork-bot+netdevbpf
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