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

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Date:   Tue, 24 May 2022 22:53:44 +0200
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Yuwei Wang <wangyuweihx@...il.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>
Cc:     davem@...emloft.net, Eric Dumazet <edumazet@...gle.com>,
        roopa@...dia.com, dsahern@...nel.org,
        秦迪 <qindi@...ff.weibo.com>,
        netdev@...r.kernel.org, yuwei wang <wangyuweihx@...mail.com>,
        razor@...ckwall.org
Subject: Re: [PATCH net-next v2] net, neigh: introduce interval_probe_time for
 periodic probe

On 5/24/22 9:13 PM, Yuwei Wang wrote:
> On Wed, 25 May 2022 at 02:07, Jakub Kicinski <kuba@...nel.org> wrote:
>> On Tue, 24 May 2022 17:32:57 +0200 Daniel Borkmann wrote:
>>> Right, maybe we could just split this into two: 1) prevent misconfig (see
>>> below), and 2) make the timeout configurable as what Yuwei has. Wdyt?
>>>
>>> diff --git a/net/core/neighbour.c b/net/core/neighbour.c
>>> index 47b6c1f0fdbb..54625287ee5b 100644
>>> --- a/net/core/neighbour.c
>>> +++ b/net/core/neighbour.c
>>> @@ -1579,7 +1579,7 @@ static void neigh_managed_work(struct work_struct *work)
>>>           list_for_each_entry(neigh, &tbl->managed_list, managed_list)
>>>                   neigh_event_send_probe(neigh, NULL, false);
>>>           queue_delayed_work(system_power_efficient_wq, &tbl->managed_work,
>>> -                          NEIGH_VAR(&tbl->parms, DELAY_PROBE_TIME));
>>> +                          max(NEIGH_VAR(&tbl->parms, DELAY_PROBE_TIME), HZ));
>>>           write_unlock_bh(&tbl->lock);
>>>    }
>>
>> FWIW that was my reaction as well. Let's do that unless someone
>> disagrees.
> 
> I agree too, so there will be as following parts:
> 1) prevent misconfig by offering a minimum value
> 2) separate the params `INTERVAL_PROBE_TIME` as the probe interval for
> `MANAGED` neigh

Ok.

> 3) notify the change of `INTERVAL_PROBE_TIME` and set the driver poll interval
> according to `INTERVAL_PROBE_TIME` instead of `DELAY_PROBE_TIME`
> 
> I still have doubt about whether we need part 3, or if exist this scenario:
> - the NIC offloading the data plane.
> - the driver needs periodically poll the device for neighbours activity
> 
> May I ask for further explanation?

Well, but for that case we would need some in-tree driver users of managed neigh
first, and they can probably drive it according to their needs if they require a
notifier message. Are you saying you are panning to convert the mlx one over to
use managed neigh?

Thanks,
Daniel