netdev - RE: [PATCH net-next 2/2] bnx2x: add RSS capability for GRE traffic

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Date:	Tue, 19 Mar 2013 13:43:27 +0000
From:	"Dmitry Kravkov" <dmitry@...adcom.com>
To:	"Eric Dumazet" <eric.dumazet@...il.com>,
	Maciej Żenczykowski <maze@...gle.com>
cc:	"davem@...emloft.net" <davem@...emloft.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"Eilon Greenstein" <eilong@...adcom.com>,
	"Tom Herbert" <therbert@...gle.com>
Subject: RE: [PATCH net-next 2/2] bnx2x: add RSS capability for GRE
 traffic

> -----Original Message-----
> From: Eric Dumazet [mailto:eric.dumazet@...il.com]
> Sent: Tuesday, March 19, 2013 2:26 PM
> To: Maciej Żenczykowski
> Cc: Dmitry Kravkov; davem@...emloft.net; netdev@...r.kernel.org; Eilon Greenstein; Tom Herbert
> Subject: Re: [PATCH net-next 2/2] bnx2x: add RSS capability for GRE traffic
> 
> Please Maciej do not top post on lkml or netdev mailing lists.
> 
> On Tue, 2013-03-19 at 02:18 -0700, Maciej Żenczykowski wrote:
> > Can the HW calculate and return a 1s complement sum of the entire
> > packet (or a large portion there-of)?
> > Fixing that up to be only of the outer IPv4, inner IPv4 and inner TCP
> > relevant portions should still be simpler (well faster) than
> > calculating the TCP checksum.
> > I'm pretty sure that some relationship between 1s complement sum of
> > all bytes, outer IPv4 checksum, inner IPv4 checksum and TCP checksum
> > could be pulled out of a hat with some deeper thought.  (similarly for
> > IPv4/GRE/IPv6/TCP and other combinations)
> >
> > What portions of the packet can the HW/FW [partially] checksum - and
> > return the value to the driver for further processing?
> > Can it return 1s complement sum of data portion of outer IPv4 (ie. in
> > IPv4/GRE/IPv4/TCP return a 1s complement sum of GRE/IPv4/TCP bytes)
> >
> 
> I assume Dmitry was speaking of this possibility, and our stack should
> handle this just fine.

In case of tunneling bnx2x HW can not provide csum of any portion of the packet.
Flag for XSUM_NO_VALIDATION on cqe will be set for all gre packets.
As a result driver will leave:
skb->ip_summed = CHECKSUM_NONE;

> 
> NIC providing these kind of checksums set :
> 
> skb->ip_summed = CHECKSUM_COMPLETE;
> skb->csum = csum;
> 
> before feeding the packet to the stack.
> 
> When we pull some header, we have to call skb_postpull_rcsum()
> to adjust the skb->csum so that final check can be done.
> 
> About 20 drivers currently provide these kind of checksumming.
>