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

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Message-ID: <20171004180715.GH1895@nanopsycho>
Date:   Wed, 4 Oct 2017 20:07:15 +0200
From:   Jiri Pirko <jiri@...nulli.us>
To:     Tom Herbert <tom@...bertland.com>
Cc:     Simon Horman <simon.horman@...ronome.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 05:52:54PM CEST, tom@...bertland.com wrote:
>On Wed, Oct 4, 2017 at 1:15 AM, Jiri Pirko <jiri@...nulli.us> wrote:
>> 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.
>
>Those are not technical arguments. As I already mentioned, I don't
>like it when we add stuff for the benefit of a 1% use case that
>negatively impacts the rest of the 99% cases which is what I believe
>is happening here.

Yeah. I just wanted the flow dissector to stay compact. But if needed,
could be split. I just fear that it will become a mess that's all.


>
>> Does not make sense in the most of the cases as the
>> dissection state would have to be carried in between calls.
>
>Please elaborate. This code is being moved into __skb_flow_dissect, so
>the functionality was already there. I don't see any description in
>this discussion that things were broken and that this patch is a
>necessary fix.

Yeah, you are right.


>
>Thanks,
>Tom