netdev - Re: [ovs-dev] [PATCH] tests: fix reference output for meter offload stats

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Date:   Fri, 7 Oct 2022 11:59:42 -0400
From:   Jamal Hadi Salim <jhs@...atatu.com>
To:     Marcelo Leitner <mleitner@...hat.com>
Cc:     Davide Caratti <dcaratti@...hat.com>,
        Ilya Maximets <i.maximets@....org>,
        Eelco Chaudron <echaudro@...hat.com>,
        Tianyu Yuan <tianyu.yuan@...igine.com>,
        Simon Horman <simon.horman@...igine.com>, dev@...nvswitch.org,
        oss-drivers <oss-drivers@...igine.com>, netdev@...r.kernel.org,
        Cong Wang <xiyou.wangcong@...il.com>,
        Oz Shlomo <ozsh@...dia.com>, Paul Blakey <paulb@...dia.com>
Subject: Re: [ovs-dev] [PATCH] tests: fix reference output for meter offload stats

On Fri, Oct 7, 2022 at 11:01 AM Marcelo Leitner <mleitner@...hat.com> wrote:
>
> On Fri, Oct 07, 2022 at 04:39:25PM +0200, Davide Caratti wrote:
> > On Fri, Oct 7, 2022 at 3:21 PM Marcelo Leitner <mleitner@...hat.com> wrote:
> > >
> > > (+TC folks and netdev@)
> > >
> > > On Fri, Oct 07, 2022 at 02:42:56PM +0200, Ilya Maximets wrote:
> > > > On 10/7/22 13:37, Eelco Chaudron wrote:
> >
> > [...]
> >
> > > I don't see how we could achieve this without breaking much of the
> > > user experience.
> > >
> > > >
> > > > - or create something like act_count - a dummy action that only
> > > >   counts packets, and put it in every datapath action from OVS.
> > >
> > > This seems the easiest and best way forward IMHO. It's actually the
> > > 3rd option below but "on demand", considering that tc will already use
> > > the stats of the first action as the flow stats (in
> > > tcf_exts_dump_stats()), then we can patch ovs to add such action if a
> > > meter is also being used (or perhaps even always, because other
> > > actions may also drop packets, and for OVS we would really be at the
> > > 3rd option below).
> >
> > Correct me if I'm wrong, but actually act_gact action with "pipe"
> > control action should already do this counting job.
>
> act_gact is so transparent that I never see it/remembers about it :)
> Yup, although it's not offloadabe with pipe control actio AFAICT.
>

It's mostly how people who offload (not sure about OVS) do it;
example some of the switches out there.
The action index, whatever that action is, could be easily mapped
to a stats index in hardware. If you are sharing action instances
(eg policer index 32) across multiple flows then of course in hw
you are using only that one instance of the meter. If you want
to have extra stats that differentiate between the flows then
add a gact (PIPE as Davide mentioned) and the only thing it
will do is count and nothing else.

cheers,
jamal