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

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Date:   Thu, 28 Jun 2018 08:15:46 +0200
From:   Jiri Pirko <jiri@...nulli.us>
To:     Jakub Kicinski <jakub.kicinski@...ronome.com>
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

Wed, Jun 27, 2018 at 08:36:24PM CEST, jakub.kicinski@...ronome.com wrote:
>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...

This looks fine to me.

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