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

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Message-ID: <20130723152735.GA28966@redhat.com>
Date:	Tue, 23 Jul 2013 18:27:35 +0300
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Stephen Hemminger <stephen@...workplumber.org>
Cc:	Jason Wang <jasowang@...hat.com>, davem@...emloft.net,
	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, Jul 23, 2013 at 08:17:27AM -0700, 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

I don't think there's a behavior change: vlan is still linearized
into the buffer. It's just done more efficiently.
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