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

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Date:	Mon, 23 May 2011 09:26:59 +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 8:38 AM, Changli Gao <xiaosuo@...il.com> wrote:
> 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.
>

For ip:
localhost ~ # ip link add link eth0 vlan1 type vlan help
Usage: ... vlan id VLANID [ FLAG-LIST ]
                          [ ingress-qos-map QOS-MAP ] [ egress-qos-map QOS-MAP ]

VLANID := 0-4095
FLAG-LIST := [ FLAG-LIST ] FLAG
FLAG := [ reorder_hdr { on | off } ] [ gvrp { on | off } ]
        [ loose_binding { on | off } ]
QOS-MAP := [ QOS-MAP ] QOS-MAPPING
QOS-MAPPING := FROM:TO

After checking the code, I found reorder_hdr is off by default.

In another side, is there a specification which defines the hw-accel-vlan-rx?

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