netdev - Re: [patch net-next 00/10] net: allow user specify TC filter HW stats type

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Date:   Mon, 24 Feb 2020 14:11:01 +0100
From:   Jiri Pirko <jiri@...nulli.us>
To:     Edward Cree <ecree@...arflare.com>
Cc:     Jakub Kicinski <kuba@...nel.org>, 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, pablo@...filter.org, mlxsw@...lanox.com
Subject: Re: [patch net-next 00/10] net: allow user specify TC filter HW
 stats type

Mon, Feb 24, 2020 at 12:38:20PM CET, ecree@...arflare.com wrote:
>On 22/02/2020 06:38, Jiri Pirko wrote:
>> Fri, Feb 21, 2020 at 07:22:00PM CET, kuba@...nel.org wrote:
>>> Hmm, but the statistics are on actions, it feels a little bit like we
>>> are perpetuating the mistake of counting on filters here.
>> You are right, the stats in tc are per-action. However, in both mlxsw
>> and mlx5, the stats are per-filter. What hw_stats does is that it
>> basically allows the user to set the type for all the actions in the
>> filter at once.
>>
>> Could you imagine a usecase that would use different HW stats type for
>> different actions in one action-chain?
>Potentially a user could only want stats on one action and disable them
> on another.  For instance, if their action chain does delivery to the
> 'customer' and also mirrors the packets for monitoring, they might only
> want stats on the first delivery (e.g. for billing) and not want to
> waste a counter on the mirror.

Okay.


>
>> Plus, if the fine grained setup is ever needed, the hw_stats could be in
>> future easilyt extended to be specified per-action too overriding
>> the per-filter setup only for specific action. What do you think?
>I think this is improper; the stats type should be defined per-action in
> the uapi, even if userland initially only has UI to set it across the
> entire filter.  (I imagine `tc action` would grow the corresponding UI
> pretty quickly.)  Then on the driver side, you must determine whether
> your hardware can support the user's request, and if not, return an
> appropriate error code.
>
>Let's try not to encourage people (users, future HW & driver developers)
> to keep thinking of stats as per-filter entities.

Okay, but in that case, it does not make sense to have "UI to set it
across the entire filter". The UI would have to set it per-action too.
Othewise it would make people think it is per-filter entity.
But I guess the tc cmdline is chatty already an it can take other
repetitive cmdline options.

What do you think?


Thanks!