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

[Paolo Abeni <pabeni@redhat.com>]

On Fri, 2016-01-08 at 18:44 -0800, pravin shelar wrote:
> On Fri, Jan 8, 2016 at 4:42 PM, Jesse Gross <jesse@kernel.org> wrote:
> > On Fri, Jan 8, 2016 at 2:53 PM, pravin shelar <pshelar@ovn.org> wrote:
> >> On Fri, Jan 8, 2016 at 1:50 PM, Paolo Abeni <pabeni@redhat.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