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

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Message-ID: <CAOrHB_DL6DpyoLYZroccPR7mjUuMM-JN6p-=o6XE53Ltb_Cq0w@mail.gmail.com>
Date:	Mon, 11 Jan 2016 16:34:25 -0800
From:	pravin shelar <pshelar@....org>
To:	Paolo Abeni <pabeni@...hat.com>
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 Mon, Jan 11, 2016 at 12:43 AM, Paolo Abeni <pabeni@...hat.com> wrote:
> 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?
>

If the final implementation is going to change alot, then I do not see
much value in this change going in first.