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

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Date:   Fri, 7 Oct 2022 10:37:15 -0700
From:   Marcelo Leitner <mleitner@...hat.com>
To:     Jamal Hadi Salim <jhs@...atatu.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 07, 2022 at 11:59:42AM -0400, Jamal Hadi Salim wrote:
> 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.

You mean with OK, DROP, TRAP or GOTO actions, right?

Because for PIPE, it has:
                } else if (is_tcf_gact_pipe(act)) {
                        NL_SET_ERR_MSG_MOD(extack, "Offload of
\"pipe\" action is not supported");
                        return -EOPNOTSUPP;

Or maybe I'm missing something.

> 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.

Yup, makes sense. And talking with Ilya, that's what OVS already does for DPDK
as well.

Thanks,
Marcelo