On Wed, 2015-07-29 at 13:49 -0700, Tom Herbert wrote:

The intent of this function was to produce a consistent hash for both
directions of a flow. However, since we added more inputs to the flow
hashing (IPv6 flow labels for instance) in a lot of cases we won't get
the same hash computed for each direction anyway. Also, there is no
defined correlation between the hashes computed in each direction of a
flow.

This patch removes the function since it is not providing significant
value and is expensive to be called for every packet. If there are
ever users of the flow_hash_from_keys that did require consistency
they can swap addresses and ports as needed in the flow_keys before
calling flow_hash_from_keys.

Have you tested this change with conntracking and RPS enabled ?

This was whole point from commit b249dcb82d327e41

I guess difference is even bigger today after removal of central
conntracking lock.