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 18:25:25 +0100
From:   Pablo Neira Ayuso <pablo@...filter.org>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     Edward Cree <ecree@...arflare.com>, 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 Mon, Mar 02, 2020 at 02:49:28PM -0800, Jakub Kicinski wrote:
> On Mon, 2 Mar 2020 22:46:59 +0100 Pablo Neira Ayuso wrote:
[...]
> > The real question is: if you think this tc counter+action scheme can
> > be used by netfilter, then please explain how.
> 
> In Jiri's latest patch set the counter type is per action, so just
> "merge right" the counter info into the next action and the models 
> are converted.

The input "merge right" approach might work.

> If user is silly and has multiple counter actions in a row - the
> pipe/no-op action comes into play (that isn't part of this set, 
> as Jiri said).

Probably gact pipe action with counters can be mapped to the counter
action that netfilter needs. Is this a valid use-case you consider for
the tc hardware offload?

> Can you give us examples of what wouldn't work? Can you for instance
> share the counter across rules?

Yes, there might be counters that are shared accross rules, see
nfacct. Two different rules might refer to the same counter, IIRC
there is a way to do this in tc too.

> Also neither proposal addresses the problem of reporting _different_
> counter values at different stages in the pipeline, i.e. moving from
> stats per flow to per action. But nobody seems to be willing to work 
> on that.

You mean, in case that different counter types are specified, eg. one
action using delayed and another action using immediate?

> AFAICT with Jiri's change we only need one check in the drivers to
> convert from old scheme to new, with explicit action we need two
> (additional one being ignoring the counter action). Not a big deal,
> but 1 is less than 2 🤷‍♂️

What changes are expected to retrieve counter stats?

Will per-flow stats remain in place after this place?

Thank you.