netdev - Re: [PATCH net-next v2] net, neigh: introduce interval_probe

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Date:   Tue, 24 May 2022 12:41:45 +0200
From:   Paolo Abeni <pabeni@...hat.com>
To:     Yuwei Wang <wangyuweihx@...il.com>
Cc:     davem@...emloft.net, Jakub Kicinski <kuba@...nel.org>,
        Eric Dumazet <edumazet@...gle.com>, daniel@...earbox.net,
        roopa@...dia.com, dsahern@...nel.org,
        秦迪 <qindi@...ff.weibo.com>,
        netdev@...r.kernel.org
Subject: Re: [PATCH net-next v2] net, neigh: introduce interval_probe_time
 for periodic probe

On Tue, 2022-05-24 at 17:38 +0800, Yuwei Wang wrote:
> On Tue, 24 May 2022 at 16:38, Paolo Abeni <pabeni@...hat.com> wrote:
> > 
> > On Sun, 2022-05-22 at 03:17 +0000, Yuwei Wang wrote:
> > 
> > > diff --git a/include/net/netevent.h b/include/net/netevent.h
> > > index 4107016c3bb4..121df77d653e 100644
> > > --- a/include/net/netevent.h
> > > +++ b/include/net/netevent.h
> > > @@ -26,6 +26,7 @@ enum netevent_notif_type {
> > >       NETEVENT_NEIGH_UPDATE = 1, /* arg is struct neighbour ptr */
> > >       NETEVENT_REDIRECT,         /* arg is struct netevent_redirect ptr */
> > >       NETEVENT_DELAY_PROBE_TIME_UPDATE, /* arg is struct neigh_parms ptr */
> > > +     NETEVENT_INTERVAL_PROBE_TIME_UPDATE, /* arg is struct neigh_parms ptr */
> > 
> > Are you sure we need to notify the drivers about this parameter change?
> > The host will periodically resolve the neighbours, and that should work
> > regardless of the NIC offload. I think we don't need additional
> > notifications.
> > 
> 
> `mlxsw_sp_router_netevent_event` in
> drivers/net/ethernet/mellanox/mlx5/core/en/rep/neigh.c and
> `mlx5e_rep_netevent_event` in
> drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c still
> use `NETEVENT_DELAY_PROBE_TIME_UPDATE` to receive the update event of
> `DELAY_PROBE_TIME` as the probe interval.
> 
> I think we are supposed to replace `NETEVENT_DELAY_PROBE_TIME_UPDATE` with
> `NETEVENT_INTERVAL_PROBE_TIME_UPDATE` after this patch is merged.

AFAICS the event notification is to let neigh_timer_handler() cope
properly with NIC offloading the data plane.

In such scenario packets (forwarded by the NIC) don't reach the host,
and neigh->confirmed can be untouched for a long time fooling
neigh_timer_handler() into a timeout.

The event notification allows the NIC to perform the correct actions to
avoid such timeout.

In case of MANAGED neighbour, the host is periodically sending probe
request, and both req/replies should not be offloaded. AFAICS no action
is expected from the NIC to cope with INTERVAL_PROBE_TIME changes.

Cheers,

Paolo