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

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Message-ID: <20171004080856.GB6378@netronome.com>
Date:   Wed, 4 Oct 2017 10:08:57 +0200
From:   Simon Horman <simon.horman@...ronome.com>
To:     Tom Herbert <tom@...bertland.com>
Cc:     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

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.