netdev - Re: [RFC] dev->refcnt long term holder

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Message-ID: <20091116110207.08b60c81@nehalam>
Date:	Mon, 16 Nov 2009 11:02:07 -0800
From:	Stephen Hemminger <shemminger@...tta.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	"David S. Miller" <davem@...emloft.net>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	Linux Netdev List <netdev@...r.kernel.org>
Subject: Re: [RFC] dev->refcnt long term holder

On Mon, 16 Nov 2009 19:01:37 +0100
Eric Dumazet <eric.dumazet@...il.com> wrote:

> time ip link del eth3.103 ; time ip link del eth3.104 ; time ip link del eth3.105
> 
> real	0m0.266s
> user	0m0.000s
> sys	0m0.001s
> 
> real	0m0.770s
> user	0m0.000s
> sys	0m0.000s
> 
> real	0m1.022s
> user	0m0.000s
> sys	0m0.000s
> 
> 
> One problem of current schem in vlan dismantle phase is the
> holding of device done by following chain :
> 
> vlan_dev_stop() ->
> 	netif_carrier_off(dev) ->
> 		linkwatch_fire_event(dev) ->
> 			dev_hold() ...
> 
> And __linkwatch_run_queue() run up to one second later...
> 
> Is following patch one way to avoid the problem, or should
> we add a new linkwatch_forgetpro_device(dev) method to immediately
> release the device reference (and unlink device from the list) ?
> (This would probably need a doubly linked list instead of single link list)

Or both..

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