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

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Date:	Tue, 19 Mar 2013 02:18:06 -0700
From:	Maciej Żenczykowski <maze@...gle.com>
To:	Dmitry Kravkov <dmitry@...adcom.com>
Cc:	Eric Dumazet <eric.dumazet@...il.com>,
	"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

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)

Maciej Żenczykowski, Kernel Networking Developer @ Google

On Mon, Mar 18, 2013 at 11:30 PM, Dmitry Kravkov <dmitry@...adcom.com> wrote:
>> -----Original Message-----
>> From: netdev-owner@...r.kernel.org [mailto:netdev-owner@...r.kernel.org] On Behalf Of Eric Dumazet
>> Sent: Tuesday, March 19, 2013 2:08 AM
>> To: Dmitry Kravkov
>> Cc: davem@...emloft.net; netdev@...r.kernel.org; Eilon Greenstein; Tom Herbert; Maciej Żenczykowski
>> Subject: Re: [PATCH net-next 2/2] bnx2x: add RSS capability for GRE traffic
>>
>> On Mon, 2013-03-18 at 18:51 +0200, Dmitry Kravkov wrote:
>> > The patch drives FW to perform RSS for GRE traffic,
>> > based on inner headers.
>> >
>> > Signed-off-by: Dmitry Kravkov <dmitry@...adcom.com>
>> > Signed-off-by: Eilon Greenstein <eilong@...adcom.com>
>> > ---
>> >  drivers/net/ethernet/broadcom/bnx2x/bnx2x_cmn.h |    3 +++
>> >  drivers/net/ethernet/broadcom/bnx2x/bnx2x_sp.c  |   23 ++++++++++++-----------
>> >  drivers/net/ethernet/broadcom/bnx2x/bnx2x_sp.h  |    9 +++++++++
>> >  3 files changed, 24 insertions(+), 11 deletions(-)
>>
>> This works very well.
>>
>> Problem is we skb_set_queue_mapping(skb, 0); in __skb_tunnel_rx()
>>
>> (this was a patch from Tom Herbert, commit
>> 693019e90ca45d881109d32c0c6d29adf03f6447 (net: reset skb queue mapping
>> when rx'ing over tunnel )
>>
>> Meaning we hit a single cpu for the GRO stuff in ip_gre.
>>
>> I have to think about it.
>>
>>
>> Another question is :
>>
>> Can bnx2x check the tcp checksum if GRE encapsulated ?
>>
> Current HW can't provide this. Probably, it's possible to separate CSUM from GRO/TPA then stack will have to handle CSUM validation for huge packets. Is it worth?
>
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