On 5/3/2016 6:29 PM, Alexander Duyck wrote:
We split the one that would be a different size off via GSO. So we end up sending up 2 frames to the device if there is going to be one piece that doesn't quite match. We split that one piece off via GSO. That is one of the reasons why I referred to it as partial GSO as all we are using the software segmentation code for is to make sure we have the GSO block consists of segments that are all the same size.
I see, so if somehow it happens a lot that the TCP stack sends down something which once segmented ends up with the last segment being of different size from the other ones we would have to call the NIC xmit function twice (BTW can we use xmit_more here?) -- which could be effecting performance, I guess.
GSO_UDP_TUNNEL_CSUM (commit 0f4f4ffa7 "net: Add GSO support for UDP tunnels with checksum") came to mark "that a device is capable of computing the UDP checksum in the encapsulating header of a UDP tunnel" -- and the way we use it here is that we do advertize that bit towards the stack for devices whose HW can **not** do that, and things work b/c of LCO (this is my understanding).
I miss something in the bigger picture here, what does this buy us? e.g vs just letting this (say) vxlan tunnel use zero checksum on the outer UDP packet, is that has something to do with RCO?
Or.
