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

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Date:   Mon, 10 Oct 2022 05:55:30 +0000
From:   Tianyu Yuan <tianyu.yuan@...igine.com>
To:     Eelco Chaudron <echaudro@...hat.com>,
        Davide Caratti <dcaratti@...hat.com>
CC:     Marcelo Leitner <mleitner@...hat.com>,
        Ilya Maximets <i.maximets@....org>,
        Simon Horman <simon.horman@...igine.com>,
        "dev@...nvswitch.org" <dev@...nvswitch.org>,
        oss-drivers <oss-drivers@...igine.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Jamal Hadi Salim <jhs@...atatu.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 10 Oct 2022, at 13:40m, Eclco Chaudron wrote:
> On 7 Oct 2022, at 16:39, 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).
> 
> Guess we have to add this extra action to each datapath flow offloaded due
> to the way flows back and forth translations are handled. Maybe we can do it
> selectively, but the code might become messier than it already is :(
> 
Thanks for your and others' comments. According to your comments, I made
a test by adding a gact with PIPE at the first place of each filter. It seems this
gact will successfully record the stats hitting this rule in sw TC datapath. But
this approach doesn't work for hw tc offload since the nic may not support
offloading this action.

In current OVS implementation, the flow stats is updated by action stats. Is
that possible to collect filter stats in kernel TC when dumping actions stats
and use this filter stats to update the flow stats in OVS. The filter stats could
also be transmitted by flower option netlink messeage.

I'm now trying to look if this will work.

Best regards,
Tianyu
> > Correct me if I'm wrong, but actually act_gact action with "pipe"
> > control action should already do this counting job.
> 
> I think we could use that, as we only use TC_ACT_GOTO_CHAIN and
> TC_ACT_SHOT. And it looks like TC_ACT_SHOT is not decoded correctly :(