netdev - Re: [PATCH net-next v9] openvswitch: enable NSH support

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Message-ID: <20170929064058.GA16145@localhost.localdomain>
Date:   Fri, 29 Sep 2017 14:40:59 +0800
From:   "Yang, Yi" <yi.y.yang@...el.com>
To:     Pravin Shelar <pshelar@....org>
Cc:     Jiri Benc <jbenc@...hat.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "dev@...nvswitch.org" <dev@...nvswitch.org>,
        "e@...g.me" <e@...g.me>,
        "davem@...emloft.net" <davem@...emloft.net>,
        Jan Scheurich <jan.scheurich@...csson.com>
Subject: Re: [PATCH net-next v9] openvswitch: enable NSH support

On Fri, Sep 29, 2017 at 02:28:38AM +0800, Pravin Shelar wrote:
> On Tue, Sep 26, 2017 at 6:39 PM, Yang, Yi <yi.y.yang@...el.com> wrote:
> > On Tue, Sep 26, 2017 at 06:49:14PM +0800, Jiri Benc wrote:
> >> On Tue, 26 Sep 2017 12:55:39 +0800, Yang, Yi wrote:
> >> > After push_nsh, the packet won't be recirculated to flow pipeline, so
> >> > key->eth.type must be set explicitly here, but for pop_nsh, the packet
> >> > will be recirculated to flow pipeline, it will be reparsed, so
> >> > key->eth.type will be set in packet parse function, we needn't handle it
> >> > in pop_nsh.
> >>
> >> This seems to be a very different approach than what we currently have.
> >> Looking at the code, the requirement after "destructive" actions such
> >> as pushing or popping headers is to recirculate.
> >
> > This is optimization proposed by Jan Scheurich, recurculating after push_nsh
> > will impact on performance, recurculating after pop_nsh is unavoidable, So
> > also cc jan.scheurich@...csson.com.
> >
> > Actucally all the keys before push_nsh are still there after push_nsh,
> > push_nsh has updated all the nsh keys, so recirculating remains avoidable.
> >
> 
> 
> We should keep existing model for this patch. Later you can submit
> optimization patch with specific use cases and performance
> improvement. So that we can evaluate code complexity and benefits.

Ok, I'll remove the below line in push_nsh and send out v11, thanks.

	key->eth.type = htons(ETH_P_NSH);

> 
> >>
> >> Setting key->eth.type to satisfy conditions in the output path without
> >> updating the rest of the key looks very hacky and fragile to me. There
> >> might be other conditions and dependencies that are not obvious.
> >> I don't think the code was written with such code path in mind.
> >>
> >> I'd like to hear what Pravin thinks about this.
> >>
> >>  Jiri