netdev - Re: [patch net-next v2 01/12] flow_offload: Introduce offload of HW stats type

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Date:   Tue, 3 Mar 2020 21:06:48 +0000
From:   Edward Cree <ecree@...arflare.com>
To:     Pablo Neira Ayuso <pablo@...filter.org>
CC:     Jakub Kicinski <kuba@...nel.org>, Jiri Pirko <jiri@...nulli.us>,
        <netdev@...r.kernel.org>, <davem@...emloft.net>,
        <saeedm@...lanox.com>, <leon@...nel.org>,
        <michael.chan@...adcom.com>, <vishal@...lsio.com>,
        <jeffrey.t.kirsher@...el.com>, <idosch@...lanox.com>,
        <aelior@...vell.com>, <peppe.cavallaro@...com>,
        <alexandre.torgue@...com>, <jhs@...atatu.com>,
        <xiyou.wangcong@...il.com>, <mlxsw@...lanox.com>,
        <netfilter-devel@...r.kernel.org>
Subject: Re: [patch net-next v2 01/12] flow_offload: Introduce offload of HW
 stats type

On 03/03/2020 20:27, Pablo Neira Ayuso wrote:
> On Tue, Mar 03, 2020 at 06:55:54PM +0000, Edward Cree wrote:
>> On 02/03/2020 22:49, Jakub Kicinski wrote:
>>> On Mon, 2 Mar 2020 22:46:59 +0100 Pablo Neira Ayuso wrote:
>>>> On Mon, Mar 02, 2020 at 12:18:52PM -0800, Jakub Kicinski wrote:
>>>>> On Mon, 2 Mar 2020 20:24:37 +0100 Pablo Neira Ayuso wrote:  
>>>>>> It looks to me that you want to restrict the API to tc for no good
>>>>>> _technical_ reason.  
>> The technical reason is that having two ways to do things where one would
>>  suffice means more code to be written, tested, debugged.  So if you want
>>  to add this you need to convince us that the existing way (a) doesn't
>>  meet your needs and (b) can't be extended to cover them.
> One single unified way to express the hardware offload for _every_
> supported frontend is the way to go. The flow_offload API provides a
> framework to model all hardware offloads for each existing front-end.
>
> I understand your motivation might be a specific front-end of your
> choice, that's fair enough.
I think we've misunderstood each other (90% my fault).

When you wrote "restrict the API to tc" I read that as "restrict growth of
 the API for flow offloading" (which I *do* want); I've now re-parsed and
 believe you meant it as "limit the API so that only tc may use it" (which
 is not my desire at all).

Thus, when I spoke of "two ways to do things" I meant that _within_ the
 (unified) flow_offload API there should be a single approach to stats
 (the counters attached to actions), to which levels above and below it
 impedance-match as necessary (e.g. by merging netfilter count actions
 onto the following action as Jakub described), rather than bundling
 two interfaces (tc-style counters and separate counter actions) into
 one API (which would mean that drivers would all need to write code to
 handle both kinds, at no gain of expressiveness).
I was *not* referring to tc and netfilter as the "two different ways", but
 I can see why you read it that way.

I hope that makes sense now.
-ed