netdev - Re: [PATCH net-next 3/6] flow_dissector: Add hash_extra field to flow

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Message-ID: <1425245265.5130.88.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Sun, 01 Mar 2015 13:27:45 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Tom Herbert <therbert@...gle.com>
Cc:	Florian Westphal <fw@...len.de>,
	David Miller <davem@...emloft.net>,
	Linux Netdev List <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next 3/6] flow_dissector: Add hash_extra field to
 flow_keys struct

On Sun, 2015-03-01 at 09:55 -0800, Tom Herbert wrote:

> Alternatively, I think we might be able to eliminate the use of
> flow_keys and flow_dissect from the qdisc code altogether. It looks
> like this is only being used to determine a hash over the addresses,
> ports, and protocol so I am thinking that we can just call
> skb_get_hash for that. Will try to post some patches soon.

Note that SFQ only stored the keys in case of a potential rehash,
and because skb->cb[] was available then.

As the rehash implies to _not_ use skb_get_hash() it is simply better to
recompute the flow key from packet, in the unlikely case we do have a
rehash.

Rehashing SFQ adds reorders, so people should think twice before using
it.


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