netdev - Re: [v3 PATCH 1/2] bonding: sync netpoll code with bridge

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Message-ID: <20101215115955.GA12559@hmsreliant.think-freely.org>
Date:	Wed, 15 Dec 2010 06:59:55 -0500
From:	Neil Horman <nhorman@...driver.com>
To:	Cong Wang <amwang@...hat.com>
Cc:	Neil Horman <nhorman@...hat.com>, linux-kernel@...r.kernel.org,
	Jiri Pirko <jpirko@...hat.com>, netdev@...r.kernel.org,
	"David S. Miller" <davem@...emloft.net>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Herbert Xu <herbert@...dor.hengli.com.au>,
	bonding-devel@...ts.sourceforge.net,
	Jay Vosburgh <fubar@...ibm.com>,
	Stephen Hemminger <shemminger@...tta.com>
Subject: Re: [v3 PATCH 1/2] bonding: sync netpoll code with bridge

On Wed, Dec 15, 2010 at 06:52:26PM +0800, Cong Wang wrote:
> 于 2010年12月09日 15:33, Cong Wang 写道:
> >On 12/08/10 21:57, Neil Horman wrote:
> >>On Wed, Dec 08, 2010 at 02:52:08AM -0500, Amerigo Wang wrote:
> >>>-    bond_for_each_slave(bond, slave, i) {
> >>>-        if ((slave->dev->priv_flags&  IFF_DISABLE_NETPOLL) ||
> >>>-            !slave->dev->netdev_ops->ndo_poll_controller)
> >>>-            ret = false;
> >>>+    np = kmalloc(sizeof(*np), GFP_KERNEL);
> >>>+    err = -ENOMEM;
> >>>+    if (!np)
> >>>+        goto out;
> >>>+
> >>>+    np->dev = slave->dev;
> >>>+    err = __netpoll_setup(np);
> >>Setting up our own netpoll instance on each slave worries me a bit.  The
> >>implication here is that, by doing so, some frames will get entirely processed
> >>by the slave.  Most notably arp frames.  That means anything that gets queued up
> >>to the arp_tx queue in __netpoll_rx will get processed during that poll event,
> >>and responded to with the mac of the slave device, rather than with the mac of
> >>the bond device, which isn't always what you want.  I think if you go with this
> >>route, you'll need to add code to netpoll_poll_dev, right before the call to
> >>service_arp_queue, to check if IFF_SLAVE is set in priv_flags, and move the list
> >>to the master device, or some such.
> >
> >
> >Good point! Will fix i
> 
> Hi, Neil,
> 
> I think we should do that in bond_poll_controller() rather than netpoll_poll_dev(),
> right? Since this is bond-specific. Does moving all arp_tx of slaves to their bond
> address your concern?
> 
Don't think that will work, because, since your using multiple netpoll instances
here, the slaves arp_tx queue will get serviced on the return from the slaves
netpoll_poll_dev call, prior to returning to the bond_poll_controller call.  In
other words, bond_poll_controller won't ever see any frames on the slaves arp_tx
queue to migrate, since they will have already been responded to by the slave
directly.
Neil

> Thanks!
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