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

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Message-ID: <20130723081727.69766d27@nehalam.linuxnetplumber.net>
Date:	Tue, 23 Jul 2013 08:17:27 -0700
From:	Stephen Hemminger <stephen@...workplumber.org>
To:	Jason Wang <jasowang@...hat.com>
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 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
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