From mboxrd@z Thu Jan  1 00:00:00 1970
From: David Miller <davem@davemloft.net>
Subject: Re: [patch net-next v3] tc: introduce OpenFlow classifier
Date: Sun, 12 Apr 2015 19:44:43 -0400 (EDT)
Message-ID: <20150412.194443.1571071793033525091.davem@davemloft.net>
References: <20150410124517.GC2021@nanopsycho.orion>
	<20150411161223.GA802@Alexeis-MBP.westell.com>
	<20150412075351.GA2112@nanopsycho.orion>
Mime-Version: 1.0
Content-Type: Text/Plain; charset=us-ascii
Content-Transfer-Encoding: 7bit
Cc: alexei.starovoitov@gmail.com, netdev@vger.kernel.org,
	jhs@mojatatu.com, tgraf@suug.ch, jesse@nicira.com
To: jiri@resnulli.us
Return-path: <netdev-owner@vger.kernel.org>
Received: from shards.monkeyblade.net ([149.20.54.216]:47837 "EHLO
	shards.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1752269AbbDLXor (ORCPT
	<rfc822;netdev@vger.kernel.org>); Sun, 12 Apr 2015 19:44:47 -0400
In-Reply-To: <20150412075351.GA2112@nanopsycho.orion>
Sender: netdev-owner@vger.kernel.org
List-ID: <netdev.vger.kernel.org>

From: Jiri Pirko <jiri@resnulli.us>
Date: Sun, 12 Apr 2015 09:53:51 +0200

> Sat, Apr 11, 2015 at 06:12:25PM CEST, alexei.starovoitov@gmail.com wrote:
>>On Fri, Apr 10, 2015 at 02:45:17PM +0200, Jiri Pirko wrote:
>>> Okay. That was misunderstanding. I was thinking about using existing
>>> flow_dissect. There are couple things which I'm scared of:
>>> - there are eventually many fields to be added to dissection function and to
>>>   the structure as well. Not sure how acceptable that would be for
>>>   performance reasons when flow_dissect is used by different users...
>>
>>I share the same concern. I think flow_dissect is too performance
>>critical to reuse by expanding 'struct flow_keys'.
>>I think it would be better to generalize ovs's key_extract() into
>>common piece of code that TC classifier and ovs datapath can use.
>>It uses kernel internal 'struct sw_flow_key' which we can tweak to
>>accommodate more users. It's already gigantic at 392 bytes, so
>>split and a bit of diet would help too.
> 
> Yep, those are few next topics on my agenda.

This argument kinda ignores the fact that full flow dissection is run
on _every_ single RX packet on basically all Intel chipsets.

Therefore, I cannot take seriously someone saying that it is too much
overhead for a classifier.

And if it is that expensive, fix it, because that helps everyone not
just your special thing.