netdev - Re: [PATCH net-next 2/2] flow_dissector: dissect tunnel info

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Message-ID: <20171004081558.GE1895@nanopsycho>
Date:   Wed, 4 Oct 2017 10:15:58 +0200
From:   Jiri Pirko <jiri@...nulli.us>
To:     Simon Horman <simon.horman@...ronome.com>
Cc:     Tom Herbert <tom@...bertland.com>,
        David Miller <davem@...emloft.net>,
        Jiri Pirko <jiri@...lanox.com>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        oss-drivers@...ronome.com
Subject: Re: [PATCH net-next 2/2] flow_dissector: dissect tunnel info

Wed, Oct 04, 2017 at 10:08:57AM CEST, simon.horman@...ronome.com wrote:
>On Tue, Oct 03, 2017 at 11:17:46AM -0700, Tom Herbert wrote:
>> On Tue, Oct 3, 2017 at 2:40 AM, Simon Horman <simon.horman@...ronome.com> wrote:
>> > On Mon, Oct 02, 2017 at 01:37:55PM -0700, Tom Herbert wrote:
>> >> On Mon, Oct 2, 2017 at 1:41 AM, Simon Horman <simon.horman@...ronome.com> wrote:
>> >> > Move dissection of tunnel info from the flower classifier to the flow
>> >> > dissector where all other dissection occurs.  This should not have any
>> >> > behavioural affect on other users of the flow dissector.
>> >
>> > ...
>> 
>> > I feel that we are circling back the perennial issue of flower using the
>> > flow dissector in a somewhat broader/different way than many/all other
>> > users of the flow dissector.
>> >
>> Simon,
>> 
>> It's more like __skb_flow_dissect is already an incredibly complex
>> function and because of that it's difficult to maintain. We need to
>> measure changes against that fact. For this patch, there is precisely
>> one user (cls_flower.c) and it's not at all clear to me if there will
>> be ever any more (e.g. for hashing we don't need tunnel info). IMO, it
>> should be just as easy and less convolution for everyone to have
>> flower call __skb_flow_dissect_tunnel_info directly and not call if
>> from __skb_flow_dissect.
>
>Hi Tom,
>
>my original suggestion was just that, but Jiri indicated a strong preference
>for the approach taken by this patch. I think we need to widen the
>participants in this discussion.

I like the __skb_flow_dissect to be the function to call and it will do
the job according to the configuration. I don't like to split in
multiple calls. Does not make sense in the most of the cases as the
dissection state would have to be carried in between calls.