netdev - Re: [PATCH net-next v2] gtp: add notification mechanism

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Message-ID: <bd834ad7-b06e-69f0-40a6-5f4a21a1eba2@6wind.com>
Date:   Wed, 26 Aug 2020 09:47:54 +0200
From:   Nicolas Dichtel <nicolas.dichtel@...nd.com>
To:     Harald Welte <laforge@...monks.org>
Cc:     davem@...emloft.net, kuba@...nel.org, pablo@...filter.org,
        osmocom-net-gprs@...ts.osmocom.org, netdev@...r.kernel.org,
        Gabriel Ganne <gabriel.ganne@...nd.com>
Subject: Re: [PATCH net-next v2] gtp: add notification mechanism

Le 25/08/2020 à 19:01, Harald Welte a écrit :
> Hi Nicolas,
> 
> thanks a lot for your patch.
> 
> On Tue, Aug 25, 2020 at 05:57:15PM +0200, Nicolas Dichtel wrote:
>> Like all other network functions, let's notify gtp context on creation and
>> deletion.
> 
> While this may be in-line with typical kernel tunnel device practises, I am not
> convinced it is the right way to go for GTP.
> 
> Contrary to other tunneling mechansims, GTP doesn't have a 1:1 rlationship between
> tunnels and netdev's.  You can easily have tens of thousands - or even many more -
> PDP contexts (at least one per subscriber) within one "gtp0" netdev.  Also, the state
> is highly volatile.  Every time a subscriber registers/deregisters, goes in or out of
> coverage, in or out of airplane mode, etc. those PDP contexts go up and down.
> 
> Sending (unsolicited) notifications about all of those seems quite heavyweight to me.
There is no 'unsolicited' notifications with this patch. Notifications are sent
only if a userspace application has subscribed to the gtp mcast group.
ip routes or conntrack entries are notified in the same way and there could a
lot of them also (more than 100k conntrack entries for example).