netdev - RE: [PATCH net-next] loopback: sctp: add NETIF_F_SCTP

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Date:	Mon, 24 Feb 2014 14:28:48 +0000
From:	David Laight <David.Laight@...LAB.COM>
To:	'Daniel Borkmann' <dborkman@...hat.com>
CC:	"davem@...emloft.net" <davem@...emloft.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-sctp@...r.kernel.org" <linux-sctp@...r.kernel.org>
Subject: RE: [PATCH net-next] loopback: sctp: add NETIF_F_SCTP_CSUM to
 device features

From: Daniel Borkmann 
> > Maybe the _le has something to do with it.
> > Could it be bit-reversing the crc and data bytes all the time?
> > The packet will (one would hope) want the crc in the same bit-order
> > as the data, so no bit reversal is needed - just the correct logic
> > and lookup table.
> 
> Although it's a bit off-topic for this patch, but I'll have a look
> into __crc32c_le(); maybe something is just wrong with that code.

Yes it generates a nice dependency chain of:
	xor	table_b(,%reg,4),%eax
using 8 tables (256*4 bytes each).

I bet that with a little bit of pipelining a simple byte by byte
loop should manage 1 byte every two clocks (ie 1 memory cycle per
clock).

	David



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