netdev - Re: [net-next 05/19] ixgbe: Add support for UDP-encapsulated tx checksum offload

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Date:	Wed, 2 Sep 2015 23:56:46 +0300
From:	Or Gerlitz <gerlitz.or@...il.com>
To:	Tom Herbert <tom@...bertland.com>
Cc:	"Rustad, Mark D" <mark.d.rustad@...el.com>,
	"Kirsher, Jeffrey T" <jeffrey.t.kirsher@...el.com>,
	"David S. Miller" <davem@...emloft.net>,
	Linux Kernel Network Developers <netdev@...r.kernel.org>,
	"nhorman@...hat.com" <nhorman@...hat.com>,
	"sassmann@...hat.com" <sassmann@...hat.com>,
	"jogreene@...hat.com" <jogreene@...hat.com>
Subject: Re: [net-next 05/19] ixgbe: Add support for UDP-encapsulated tx
 checksum offload

On Wed, Sep 2, 2015 at 8:38 PM, Tom Herbert <tom@...bertland.com> wrote:
> On Wed, Sep 2, 2015 at 9:46 AM, Rustad, Mark D <mark.d.rustad@...el.com> wrote:
>>> On Sep 1, 2015, at 8:17 PM, Tom Herbert <tom@...bertland.com> wrote:
>>>
>>> I suspect this is not UDP-encapsulation specific, will it work with
>>> TCP/IP/IP, TCP/IP/GRE etc.?
>>
>> It could do more, but this is what has been tested up to this point.
>>
> Well, please test the those other encapsulations too! It's nice and
> all if they get the benefit, but it's really bad news if these changes
> were to screw them up (i.e. you don't want users of the GRE, IPIP to
> find out that they're now broken).
>
>>> Isn't there anyway the ixgbe could just be made to NETIF_HW_CSUM? That
>>> would be so much more straightforward and support nearly all use cases
>>> without needing to jump through all these hoops.
>>
>> Well, the description says:
>>
>>  ---
>> Note: NETIF_F_HW_CSUM is a superset of NETIF_F_IP_CSUM + NETIF_F_IPV6_CSUM.
>> It means that device can fill TCP/UDP-like checksum anywhere in the packets
>> whatever headers there might be.
>>  ---
>>
>> The device can't do whatever, wherever. There is always a limit to the offset to the inner headers that can be handled, for instance.
>>
> If the device does NETIF_F_HW_CSUM then inner/outer headers are
> irrelevant at least in the non-GSO case. All the device needs to do is
> compute the checksum from start and write the answer at the given
> offset. No protocol awareness needed in the device, no need to parse
> headers on transmit.

Tom, could you elaborate a little further on the
semantics/requirements for devices supporting NETIF_F_HW_CSUM, clearly
(as mentioned in




> I have the same complaint that ixgbe requires a bunch of driver logic
> to offload VXLAN checksum unnecessary instead of just providing
> CHECKSUM_COMPLETE which would work with any encapsulation protocol,
> require no encapsulation awareness in the device, and should be a much
> simpler driver implementation.
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