netdev - Re: [patch net-next 0/9] net: sched: introduce chain templates support with offloading to mlxsw

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Message-ID: <20180627113624.5f8d74e9@cakuba.netronome.com>
Date:   Wed, 27 Jun 2018 11:36:24 -0700
From:   Jakub Kicinski <jakub.kicinski@...ronome.com>
To:     Jiri Pirko <jiri@...nulli.us>
Cc:     Linux Netdev List <netdev@...r.kernel.org>,
        David Miller <davem@...emloft.net>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Simon Horman <simon.horman@...ronome.com>,
        John Hurley <john.hurley@...ronome.com>,
        David Ahern <dsahern@...il.com>, mlxsw@...lanox.com
Subject: Re: [patch net-next 0/9] net: sched: introduce chain templates
 support with offloading to mlxsw

On Wed, 27 Jun 2018 09:50:17 +0200, Jiri Pirko wrote:
> Tue, Jun 26, 2018 at 11:18:58PM CEST, jakub.kicinski@...ronome.com wrote:
> >On Tue, 26 Jun 2018 09:12:17 +0200, Jiri Pirko wrote:  
> >> Tue, Jun 26, 2018 at 09:00:45AM CEST, jakub.kicinski@...ronome.com wrote:  
> >> >On Mon, Jun 25, 2018 at 11:43 PM, Jiri Pirko <jiri@...nulli.us> wrote:    
> >> >> Tue, Jun 26, 2018 at 06:58:50AM CEST, jakub.kicinski@...ronome.com wrote:    
> >> >>>On Mon, 25 Jun 2018 23:01:39 +0200, Jiri Pirko wrote:    
> >> >>>> From: Jiri Pirko <jiri@...lanox.com>
> >> >>>>
> >> >>>> For the TC clsact offload these days, some of HW drivers need
> >> >>>> to hold a magic ball. The reason is, with the first inserted rule inside
> >> >>>> HW they need to guess what fields will be used for the matching. If
> >> >>>> later on this guess proves to be wrong and user adds a filter with a
> >> >>>> different field to match, there's a problem. Mlxsw resolves it now with
> >> >>>> couple of patterns. Those try to cover as many match fields as possible.
> >> >>>> This aproach is far from optimal, both performance-wise and scale-wise.
> >> >>>> Also, there is a combination of filters that in certain order won't
> >> >>>> succeed.
> >> >>>>
> >> >>>> Most of the time, when user inserts filters in chain, he knows right away
> >> >>>> how the filters are going to look like - what type and option will they
> >> >>>> have. For example, he knows that he will only insert filters of type
> >> >>>> flower matching destination IP address. He can specify a template that
> >> >>>> would cover all the filters in the chain.    
> >> >>>
> >> >>>Perhaps it's lack of sleep, but this paragraph threw me a little off
> >> >>>the track.  IIUC the goal of this set is to provide a way to inform the
> >> >>>HW about expected matches before any rule is programmed into the HW.
> >> >>>Not before any rule is added to a particular chain.  One can just use
> >> >>>the first rule in the chain to make a guess about the chain, but thanks
> >> >>>to this set user can configure *all* chains before any rules are added.    
> >> >>
> >> >> The template is per-chain. User can use template for chain x and
> >> >> not-use it for chain y. Up to him.    
> >> >
> >> >Makes sense.
> >> >
> >> >I can't help but wonder if it'd be better to associate the
> >> >constraints/rules with chains instead of creating a new "template"
> >> >object.  It seems more natural to create a chain with specific
> >> >constraints in place than add and delete template of which there can
> >> >be at most one to a chain...  Perhaps that's more about the user space
> >> >tc command line.  Anyway, not a strong objection, just a thought.    
> >> 
> >> Hmm. I don't think it is good idea. User should see the template in a
> >> "show" command per chain. We would have to have 2 show commands, one to
> >> list the template objects and one to list templates per chains. It makes
> >> things more complicated for no good reason. I think that this simple
> >> chain-lock is easier and serves the purpose.  
> >
> >Hm, I think the dump is fine, what I was thinking about was:
> >
> ># tc chain add dev dummy0 ingress chain_index 22 \
> >     ^^^^^
> >	template proto ip \
> >	^^^^^^^^
> >	flower dst_mac 00:00:00:00:00:00/00:00:00:00:FF:FF  
> 
> Okay, I got it. I see 2 issues.
> 1) user might expect to add a chain without the template. But that does
>    not make sense really. Chains are created/deleted implicitly
>    according to refcount.
> 2) there is not chain object like this available to user. Adding it just
>    for template looks odd. Also, the "filter" and "template" are very
>    much alike. They both are added to a chain, they both implicitly
>    create chain if it does not exist, etc.

Yeah, that part makes is tricky :/

> if you don't like "tc filter template add dev dummy0 ingress", how
> about:
> "tc template add dev dummy0 ingress ..."
> "tc template add dev dummy0 ingress chain 22 ..."
> that makes more sense I think.

Mmm..  how about:

 tc chaintemplate add dev dummy0 ingress...

or

 tc restrictedchain add dev dummy0 ingress chain_index XX template ...