netdev - Re: [PATCH net 1/2] macvlan: forbid L2 fowarding offload for macvtap

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Message-Id: <20140107.005747.2228695405723185015.davem@davemloft.net>
Date:	Tue, 07 Jan 2014 00:57:47 -0500 (EST)
From:	David Miller <davem@...emloft.net>
To:	jasowang@...hat.com
Cc:	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	mst@...hat.com, john.r.fastabend@...el.com, nhorman@...driver.com
Subject: Re: [PATCH net 1/2] macvlan: forbid L2 fowarding offload for
 macvtap

From: Jason Wang <jasowang@...hat.com>
Date: Tue, 07 Jan 2014 11:17:06 +0800

> On 01/07/2014 04:47 AM, David Miller wrote:
>> From: Jason Wang <jasowang@...hat.com>
>> Date: Mon,  6 Jan 2014 11:21:06 +0800
>>
>>> L2 fowarding offload will bypass the rx handler of real device. This will make
>>> the packet could not be forwarded to macvtap device. Another problem is the
>>> dev_hard_start_xmit() called for macvtap does not have any synchronization.
>>>
>>> Fix this by forbidding L2 forwarding for macvtap.
>>>
>>> Cc: John Fastabend <john.r.fastabend@...el.com>
>>> Cc: Neil Horman <nhorman@...driver.com>
>>> Signed-off-by: Jason Wang <jasowang@...hat.com>
>> I think I agree with Neil that the rx_handler change might be the best
>> way to fix this.  That change seems to have a lot of nice unintended
>> side effects, no?
> 
> Not all sides effects are nice.
> 
> One obvious issue is it disables the multiqueue macvtap transmission,
> since all queues will contend on a single qdisc lock of macvlan. And
> even more, multiqueue macvtap support creating and destroying a queue on
> demand which is not supported by L2 forwarding offload.
> 
> So L2 forwarding offload needs more fixes to let the multiqueue macvtap
> works. Currently, we really need this patch to make sure macvtap works
> as expected.

Ok I moved these two patches back to "Under Review".

These are pretty last minute and we'll need to make a decision on
what to do before Friday if you want these changes to really make
it into 3.13
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