From: Vladimir Oltean <olteanv@gmail.com>
To: David Laight <David.Laight@ACULAB.COM>
Cc: Eric Dumazet <edumazet@google.com>,
Eric Dumazet <eric.dumazet@gmail.com>,
"David S . Miller" <davem@davemloft.net>,
Jakub Kicinski <kuba@kernel.org>, netdev <netdev@vger.kernel.org>
Subject: Re: [PATCH net-next 2/2] net: optimize skb_postpull_rcsum()
Date: Fri, 3 Dec 2021 18:14:29 +0200 [thread overview]
Message-ID: <20211203161429.htqt4vuzd22rlwkf@skbuf> (raw)
In-Reply-To: <eb25fee06370430d8cd14e25dff5e653@AcuMS.aculab.com>
On Fri, Dec 03, 2021 at 02:57:04PM +0000, David Laight wrote:
> From: Vladimir Oltean
> > Sent: 02 December 2021 21:40
> ...
> > >
> > > Try replacing both ~ with -.
> > > So replace:
> > > skb->csum = ~csum_partial(start, len, ~skb->csum);
> > > with:
> > > skb->csum = -csum_partial(start, len, -skb->csum);
> > >
> > > That should geneate ~0u instead 0 (if I've got my maths right).
> >
> > Indeed, replacing both one's complement operations with two's complement
> > seems to produce correct results (consistent with old code) in all cases
> > that I am testing with (ICMP, TCP, UDP). Thanks!
>
> You need to generate (or persuade Eric to generate) a patch.
> I don't have the right source tree.
>
> Any code that does ~csum_partial() is 'dubious' unless followed
> by a check for 0.
> The two's compliment negate save the conditional - provided the
> offset of 1 can be added in earlier.
>
> David
>
> -
> Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
> Registration No: 1397386 (Wales)
>
Eric, could you please send a patch with this change?
If you want and if it helps, I can also help you reproduce this locally
using the dsa_loop mockup driver.
next prev parent reply other threads:[~2021-12-03 16:14 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 [this message]
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
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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