Re: [PATCH net-next v2] net, neigh: introduce interval_probe_time for periodic probe

From: Yuwei Wang <wangyuweihx@gmail.com>
To: Paolo Abeni <pabeni@redhat.com>
Cc: davem@davemloft.net, "Jakub Kicinski" <kuba@kernel.org>,
	"Eric Dumazet" <edumazet@google.com>,
	daniel@iogearbox.net, roopa@nvidia.com, dsahern@kernel.org,
	秦迪 <qindi@staff.weibo.com>,
	netdev@vger.kernel.org, "yuwei wang" <wangyuweihx@hotmail.com>
Subject: Re: [PATCH net-next v2] net, neigh: introduce interval_probe_time for periodic probe
Date: Tue, 24 May 2022 22:33:49 +0800	[thread overview]
Message-ID: <CANmJ_FOSfJY7VUQrxb+hX42XjiuF+WZGcbQEiSDRQiRZRBHT9g@mail.gmail.com> (raw)
In-Reply-To: <cf3188eba7e529e4f112f6a752158f38e22f4851.camel@redhat.com>

On Tue, 24 May 2022 at 18:41, Paolo Abeni <pabeni@redhat.com> wrote:
>
> On Tue, 2022-05-24 at 17:38 +0800, Yuwei Wang wrote:
> > On Tue, 24 May 2022 at 16:38, Paolo Abeni <pabeni@redhat.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.

I think `INTERVAL_PROBE_TIME` is not only for MANAGED neighbour,
if the driver needs periodically poll the device for neighbours activity,
we also should use  `INTERVAL_PROBE_TIME` rather than `DELAY_PROBE_TIME` as
the polling interval.

but as
Link: https://lore.kernel.org/netdev/20211011121238.25542-5-daniel@iogearbox.net/

> mlxsw which has similar driver-internal infrastructure
> c723c735fa6b ("mlxsw: spectrum_router: Periodically update the kernel's neigh table").
> In future, the latter could possibly reuse the NTF_MANAGED neighbors as well.

It seems that the behavior probe periodically by the driver will be
deprecated and replaced by setting the MANAGED flag.
or we can keep using `DELAY_PROBE_TIME` before it is replaced?

Look forward to your reply.

Yuwei Wang