netdev - Re: [PATCH net] openvswitch: compute needed headroom for internal vports

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Date:	Mon, 11 Jan 2016 09:43:08 +0100
From:	Paolo Abeni <pabeni@...hat.com>
To:	pravin shelar <pshelar@....org>
Cc:	Jesse Gross <jesse@...nel.org>,
	Linux Kernel Network Developers <netdev@...r.kernel.org>,
	Pravin Shelar <pshelar@...ira.com>,
	"David S. Miller" <davem@...emloft.net>,
	Flavio Leitner <fbl@...close.org>
Subject: Re: [PATCH net] openvswitch: compute needed headroom for internal
 vports

On Fri, 2016-01-08 at 18:44 -0800, pravin shelar wrote:
> On Fri, Jan 8, 2016 at 4:42 PM, Jesse Gross <jesse@...nel.org> wrote:
> > On Fri, Jan 8, 2016 at 2:53 PM, pravin shelar <pshelar@....org> wrote:
> >> On Fri, Jan 8, 2016 at 1:50 PM, Paolo Abeni <pabeni@...hat.com> wrote:
> >>> Currently the ovs internal vports always use a default needed_headroom.
> >>> This leads to a skb head copy while xmitting on ovs swith via vport
> >>> that add some kind of encapsulation (gre, geneve, etc.).
> >>>
> >>> This patch add book-keeping for the maximum needed_headroom used by
> >>> the non internal vports in any dp, updating it on vport creation and
> >>> deletion.
> >>>
> >>> Said value is than used as needed_headroom for internal vports,
> >>> avoiding the above copy.
> >>>
> >> Why is this done only for internal devices? In most common case of
> >> traffic the packet enters OVS from tap or other netdev type vport
> >> device.
> >
> > How would you influence the allocation for non-internal devices?
> 
> Today there is no way of influencing this. But we could add new
> skb-headroom parameter to netdev for packets that are received on the
> device. This new parameter could be controlled from master devices
> like OVS, Bridge, etc. To set this value we need new ndo operation. So
> that it can work on devices like tap where it would just set this new
> value and in case of ovs-internal or veth device, it can also update
> needed_headroom.

My idea was to continue working along this lines.

However I thought to get there incrementally, i.e. handle internal
vports only first. Can this be ok for you?

Cheers,

Paolo