netdev - Re: [PATCH 1/3] vlan: Do not support clearing VLAN_FLAG_REORDER

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Date:	Mon, 23 May 2011 08:38:36 +0800
From:	Changli Gao <xiaosuo@...il.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	Ben Greear <greearb@...delatech.com>,
	David Miller <davem@...emloft.net>,
	Jiri Pirko <jpirko@...hat.com>,
	Nicolas de Pesloüan 
	<nicolas.2p.debian@...il.com>, netdev@...r.kernel.org,
	shemminger@...ux-foundation.org, kaber@...sh.net, fubar@...ibm.com,
	eric.dumazet@...il.com, andy@...yhouse.net,
	Jesse Gross <jesse@...ira.com>
Subject: Re: [PATCH 1/3] vlan: Do not support clearing VLAN_FLAG_REORDER_HDR

On Mon, May 23, 2011 at 6:38 AM, Eric W. Biederman
<ebiederm@...ssion.com> wrote:
>
>> Many years ago we supported the REORDER, but we suggested disabling
>> it for most users because it was a performance drag.  Funny that now
>> it seems to be the opposite!
>
> Yes it is funny.  I looked in history a while back and what I saw was
> that REORDER was always enabled by default and it took some serious
> effort to figure out how to get vconfig to disable REORDER. ip doesn't
> admit that REORDER can be disabled at all.
>

Really?

Quoted from the manual page of vconfig
       set_flag [vlan-device] 0 | 1
              When  1,  ethernet  header  reorders  are turned on. Dumping the
              device will appear as a common ethernet  device  without  vlans.
              When  0(default)  however,  ethernet  headers are not reordered,
              which results in vlan tagged packets when  dumping  the  device.
              Usually the default gives no problems, but some packet filtering
              programs might have problems with it.

reordered is disabled by default. I also concern the performance.
Untag and then tag are expensive for the NICs which don't support
hw-accel-vlan-rx/tx.

-- 
Regards,
Changli Gao(xiaosuo@...il.com)
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