netdev - RE: [PATCH net] net: lapb: Copy the skb before sending a packet

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Date:   Tue, 2 Feb 2021 09:04:07 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Xie He' <xie.he.0141@...il.com>,
        Julian Wiedmann <jwi@...ux.ibm.com>
CC:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Linux X25 <linux-x25@...r.kernel.org>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        "Martin Schiller" <ms@....tdt.de>
Subject: RE: [PATCH net] net: lapb: Copy the skb before sending a packet

From: Xie He
> Sent: 01 February 2021 16:15
> 
> On Mon, Feb 1, 2021 at 6:10 AM Julian Wiedmann <jwi@...ux.ibm.com> wrote:
> >
> > This sounds a bit like you want skb_cow_head() ... ?
> 
> Calling "skb_cow_head" before we call "skb_clone" would indeed solve
> the problem of writes to our clones affecting clones in other parts of
> the system. But since we are still writing to the skb after
> "skb_clone", it'd still be better to replace "skb_clone" with
> "skb_copy" to avoid interference between our own clones.

What is the fastest link lapb is actually used on these days?
64k used to be 'fast' - so copying the skb isn't going to have
a noticeable effect on system performance.

We did once get a 'free' upgrade of our X.25 link from 2400 to 9600.
Probably due to the power consumption and rack space needed for
the older modem.

	David

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