linux-kernel - Re: [PATCH net-next] tuntap: hardware vlan tx support

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Message-ID: <51EF5B00.7040109@redhat.com>
Date:	Wed, 24 Jul 2013 12:41:36 +0800
From:	Jason Wang <jasowang@...hat.com>
To:	Stephen Hemminger <stephen@...workplumber.org>
CC:	davem@...emloft.net, mst@...hat.com, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, Basil Gor <basil.gor@...il.com>
Subject: Re: [PATCH net-next] tuntap: hardware vlan tx support

On 07/23/2013 11:17 PM, Stephen Hemminger wrote:
> On Tue, 23 Jul 2013 15:15:48 +0800
> Jason Wang <jasowang@...hat.com> wrote:
>
>> Inspired by commit f09e2249c4f5c7c13261ec73f5a7807076af0c8e (macvtap: restore
>> vlan header on user read). This patch adds hardware vlan tx support for
>> tuntap. This is done by copying vlan header directly into userspace in
>> tun_put_user() instead of doing it through __vlan_put_tag() in
>> dev_hard_start_xmit(). This eliminates one unnecessary memove in
>> vlan_insert_tag() for 802.1ad and 802.1q traffic.
>>
>> pktgen test shows about 20% improvement for 802.1q traffic:
>>
>> Before:
>>   662149pps 317Mb/sec (317831520bps) errors: 0
>> After:
>>   801033pps 384Mb/sec (384495840bps) errors: 0
>>
>> Cc: Basil Gor <basil.gor@...il.com>
>> Cc: Michael S. Tsirkin <mst@...hat.com>
>> Signed-off-by: Jason Wang <jasowang@...hat.com>
>
> You need to make this configurable by some mechanism, since otherwise
> it will break applications that expect current VLAN behavior
> --
>

Didn't see any breakage. Vlan id will always exist in the userspace buffer.
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