netdev - Re: [patch net-next v3] tc: introduce OpenFlow classifier

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Message-ID: <20150413082600.GA16323@casper.infradead.org>
Date:	Mon, 13 Apr 2015 09:26:00 +0100
From:	Thomas Graf <tgraf@...g.ch>
To:	Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:	David Miller <davem@...emloft.net>, jiri@...nulli.us,
	netdev@...r.kernel.org, jhs@...atatu.com, jesse@...ira.com
Subject: Re: [patch net-next v3] tc: introduce OpenFlow classifier

On 04/12/15 at 06:03pm, Alexei Starovoitov wrote:
> On Sun, Apr 12, 2015 at 08:36:18PM -0400, David Miller wrote:
> > 
> > It's easy to parameterize what flow dissector does and share code.
> 
> yes. Though I wouldn't pessimize ixgbe rx path even by single
> cycle to accommodate openflow spec. As far as I understand the
> skb_flow_dissect() job from driver point of view is to figure
> out header length for copybreak, which includes parsing encaps,
> whereas openflow stops at outer header. Even with this difference,
> it surely can be parameterized. Would be great to share if it
> doesn't cost rx anything.

A flow dissector that only extracts what's needed would benefit
everyone. I guess static keys could help here as the flow field
selection is definitely a slow path operation.

Even OVS could benefit from this eventually, it would just need
to do a full extract before the key is sent to user space.

Also, the logic to generate the wildcard mask and match on it
should be generalized as well.
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