On Wed, Jul 29, 2015 at 3:15 PM, Eric Dumazet <eric.duma...@gmail.com> wrote: > On Wed, 2015-07-29 at 14:47 -0700, Tom Herbert wrote: > >> Hi Eric, >> >> So the scenario you're thinking is conntrack in the forwarding path, >> RPS enabled (RSS not relevant), no hash from device, no IPv6 flow >> labels or any other asymmetric inputs into the flow hash? I can look >> at that, but it does make me wonder if maybe conntrack should set RFS >> for both sides to avoid any issue with asymmetric hashes. With more >> IPv6 and flow labels (which we will enable by default), asymmetric >> hashes will likely become the norm. > > Yes, but as long as the hash was done in software in our stack we could > use flow dissection and this swap() thing, regardless of the hashes > computed by the NIC or derived from IPv6 flow label. > The IPv6 flow label is now taken as input to the software hash (along with VLAN id, GRE keyid, MPLS label, etc.). Packets encapsulated in UDP also cause asymmetric hashes since the source port is used for entropy. We have no way to predict what a remote host will put into these fields, so our only recourse would be not include them in the hash if symmetric hashes are really a requirement.
> RFS wont fly here, as DDOS traffic will need more cache misses. > > -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
