netdev - Re: [PATCH net-next] flow_dissector: remove __flow_hash

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Message-ID: <1438204774.20182.109.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Wed, 29 Jul 2015 23:19:34 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Tom Herbert <tom@...bertland.com>
Cc:	davem@...emloft.net, netdev@...r.kernel.org, kernel-team@...com
Subject: Re: [PATCH net-next] flow_dissector: remove
 __flow_hash_consistentify

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.



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