netdev - Re: [PATCH net-next-2.6] net: add dev_close

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Date:	Mon, 13 Dec 2010 09:32:21 -0800
From:	Stephen Hemminger <shemminger@...tta.com>
To:	Octavian Purdila <opurdila@...acom.com>
Cc:	Eric Dumazet <eric.dumazet@...il.com>, netdev@...r.kernel.org,
	Lucian Adrian Grijincu <lucian.grijincu@...il.com>,
	Vlad Dogaru <ddvlad@...edu.org>
Subject: Re: [PATCH net-next-2.6] net: add dev_close_many

On Mon, 13 Dec 2010 19:23:26 +0200
Octavian Purdila <opurdila@...acom.com> wrote:

> From: Eric Dumazet <eric.dumazet@...il.com>
> Date: Monday 13 December 2010, 18:52:25
> 
> > Hmm, I think this solves the "rmmod dummy" case, but not the "dismantle
> > devices one by one", which is the general one (on heavy duty tunnels/ppp
> > servers)
> > 
> > I think we could use a kernel thread (a workqueue presumably), handling
> > 3 lists of devices to be dismantled, respecting one rcu grace period (or
> > rcu_barrier()) before transfert of one item from one list to following
> > one.
> > 
> > This way, each device removal could post a device to this kernel thread
> > and return to user immediately. Time of RTNL hold would be reduced
> > (calls to synchronize_rcu() would be done with RTNL not held)
> 
> We also run into the case where we have to dismantle the interfaces one by one 
> but we fix it by gathering the requests in userspace and then doing a 
> unregister_netdevice_many operation.
> 
> I like the kernel thread / workqueue idea. But we would still need 
> netdevice_unregister_many and dev_close_many right? - we put the device in the 
> unregister list in unregister_netdevice and call unregister_netdevice_many in 
> the kernel thread.

With a message based interface, there shouldn't be a need for this.
Just have one thread sending requests in user space, and one receiving
the ACK's.
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