netdev - Re: [PATCH RFC RFC] rds: Use NETDEV_UNREGISTER in rds_tcp_dev_event() (then kill NETDEV_UNREGISTER

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Date:   Fri, 16 Mar 2018 21:48:13 +0300
From:   Kirill Tkhai <ktkhai@...tuozzo.com>
To:     Sowmini Varadhan <sowmini.varadhan@...cle.com>
Cc:     santosh.shilimkar@...cle.com, davem@...emloft.net,
        netdev@...r.kernel.org, linux-rdma@...r.kernel.org,
        rds-devel@....oracle.com, edumazet@...gle.com
Subject: Re: [PATCH RFC RFC] rds: Use NETDEV_UNREGISTER in rds_tcp_dev_event()
 (then kill NETDEV_UNREGISTER_FINAL)

On 16.03.2018 21:31, Sowmini Varadhan wrote:
> On (03/16/18 21:14), Kirill Tkhai wrote:
>>
>> I did the second version and sent you. Have you tried it?
> 
> I tried it briefly, and it works for the handful of testcases
> that I tried, but I still think its very werid to register
> as both a device and a subsys, esp in the light of the 
> warning in net_namespace.h

I'll send a patch updating comment in net_namespace.h to clarify
the situation.

> Thus I have to spend some time reviewing your patch,
> and I cannot give you an answer in the next 5 minutes.

No problem, 5 minutes response never required. Thanks for
your review.

>> Calling netdevice handler for every event is more disturbing,
>> as number of events is several times bigger, than one more
>> pernet exit method.
> 
> So you are saying there are scaling constraints on subsystems
> that register for netdevice handlers. The disturbing part
> of that is that it does not scale.

It does not scale. But if we do not work on this, nothing will change.

My point about less numbers is that every namespace will call this
new pernet->exit once. So, we will have 1 new function call per one
namespace.

Let's count numbers, if we have the same functionality implemented as netdev event.
Every net namespace has loopback dev. This device will be registered
and unregistered. The event handler will be called for many events
during this actions: NETDEV_REGISTER, NETDEV_UNREGISTER, NETDEV_POST_INIT, etc, etc.

So, if we use pernet exit, it leads us to signify less number of function calls.
Just this.

Kirill