From: David Laight <David.Laight@ACULAB.COM>
To: "'Måns Rullgård'" <mans@mansr.com>, "Felix Fietkau" <nbd@nbd.name>
Cc: "linux-mips@linux-mips.org" <linux-mips@linux-mips.org>,
Netdev <netdev@vger.kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
David Miller <davem@davemloft.net>,
WireGuard mailing list <wireguard@lists.zx2c4.com>
Subject: RE: Misalignment, MIPS, and ip_hdr(skb)->version
Date: Mon, 12 Dec 2016 16:19:17 +0000 [thread overview]
Message-ID: <063D6719AE5E284EB5DD2968C1650D6DB023BF78@AcuExch.aculab.com> (raw)
In-Reply-To: <yw1x37hvykzk.fsf@unicorn.mansr.com>
From: M=E5ns Rullg=E5rd
> Sent: 10 December 2016 13:25
...
> I solved this problem in an Ethernet driver by copying the initial part
> of the packet to an aligned skb and appending the remainder using
> skb_add_rx_frag(). The kernel network stack only cares about the
> headers, so the alignment of the packet payload doesn't matter.
That rather depends on where the packet payload ends up.
It is likely that it will be copied to userspace (or maybe
into some aligned kernel buffer).
In which case you get an expensive misaligned copy.
Encapsulation protocols not using headers that are multiples
of 4 bytes is as stupid as ethernet hardware that can't place
the mac address on a 4n+2 boundary.
The latter is particularly stupid when it happens on embedded
silicon with a processor that can only do aligned memory accesses.
What do the hardware engineers think the ethernet interface will
be used for!
David
next prev parent reply other threads:[~2016-12-12 16:13 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-12-07 18:35 Jason A. Donenfeld
2016-12-07 18:47 ` Dave Taht
2016-12-07 18:51 ` David Miller
2016-12-07 18:54 ` Jason A. Donenfeld
2016-12-07 19:52 ` David Miller
2016-12-08 0:29 ` Jason A. Donenfeld
2016-12-08 0:37 ` David Miller
2016-12-08 22:20 ` Jason A. Donenfeld
2016-12-08 23:14 ` David Miller
2016-12-11 8:07 ` Willy Tarreau
2016-12-11 10:47 ` Måns Rullgård
2016-12-10 12:25 ` Felix Fietkau
2016-12-10 13:25 ` Måns Rullgård
2016-12-10 20:09 ` Felix Fietkau
2016-12-10 20:32 ` Måns Rullgård
2016-12-10 20:36 ` Felix Fietkau
2016-12-12 16:19 ` David Laight [this message]
2016-12-12 16:31 ` Måns Rullgård
2016-12-08 0:30 ` Hannes Frederic Sowa
2016-12-08 4:34 ` Daniel Kahn Gillmor
2016-12-09 11:26 ` Jiri Benc
2016-12-10 22:18 ` Dan Lüdtke
2016-12-11 7:15 ` Greg KH
2016-12-11 14:50 ` Jason A. Donenfeld
2016-12-11 15:30 ` Andrew Lunn
2016-12-11 15:37 ` Jason A. Donenfeld
2016-12-11 16:44 ` Willy Tarreau
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