netdev - RE: [PATCH net-next] hv_netvsc: Increase delay for RNDIS_STATUS_NETWORK

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Message-ID: <BN1PR0301MB07700DD7E77C7B71C650B37DCAD60@BN1PR0301MB0770.namprd03.prod.outlook.com>
Date:	Tue, 9 Feb 2016 15:31:34 +0000
From:	Haiyang Zhang <haiyangz@...rosoft.com>
To:	David Miller <davem@...emloft.net>
CC:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	KY Srinivasan <kys@...rosoft.com>,
	"olaf@...fle.de" <olaf@...fle.de>,
	"vkuznets@...hat.com" <vkuznets@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"driverdev-devel@...uxdriverproject.org" 
	<driverdev-devel@...uxdriverproject.org>
Subject: RE: [PATCH net-next] hv_netvsc: Increase delay for
 RNDIS_STATUS_NETWORK_CHANGE



> -----Original Message-----
> From: David Miller [mailto:davem@...emloft.net]
> Sent: Tuesday, February 9, 2016 5:05 AM
> To: Haiyang Zhang <haiyangz@...rosoft.com>
> Cc: netdev@...r.kernel.org; KY Srinivasan <kys@...rosoft.com>;
> olaf@...fle.de; vkuznets@...hat.com; linux-kernel@...r.kernel.org;
> driverdev-devel@...uxdriverproject.org
> Subject: Re: [PATCH net-next] hv_netvsc: Increase delay for
> RNDIS_STATUS_NETWORK_CHANGE
> 
> From: Haiyang Zhang <haiyangz@...rosoft.com>
> Date: Tue,  2 Feb 2016 16:15:56 -0800
> 
> > We simulates a link down period for RNDIS_STATUS_NETWORK_CHANGE
> > message to trigger DHCP renew. User daemons may need multiple seconds
> > to trigger the link down event. (e.g. ifplugd: 5sec, network-manager:
> > 4sec.) So update this link down period to 10 sec to properly trigger DHCP
> renew.
> >
> > Signed-off-by: Haiyang Zhang <haiyangz@...rosoft.com>
> 
> Two things look really bad about this to me:
> 
> 1) Any value you choose is arbitrary.  If some new network configuration
> daemon
>    is slower, you will have to change this value again.
> 
>    This is _NOT_ sustainable in the long term.
> 
> 2) It is completely unclear to me why this driver needs to delay at all or
>    wait for anything.  I see no other driver having to deal with this issue.
> 
> Until you address both of these points I am not going to apply this patch.

1) I share your concern as well. Is there a universal way to immediately trigger 
DHCP renew of all current and future daemons with a single event from kernel? 
If not, can we put the delay (RNDIS_STATUS_NETWORK_CHANGE only) into a 
tunable variable of this driver?

2) We used to have the call_usermodehelper "/etc/init.d/network restart" to 
trigger DHCP renew. In commit 27a70af3f4, Vitaly has replaced it with the current 
code that updates the link status with at least 2 seconds interval, so that the 
"link_watch infrastructure" can send notification out. link_watch infrastructure 
only sends one notification per second.

Thanks,
- Haiyang