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

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Date:	Tue, 12 Jan 2016 11:20:08 -0800
From:	Jesse Gross <jesse@...nel.org>
To:	pravin shelar <pshelar@....org>
Cc:	Paolo Abeni <pabeni@...hat.com>,
	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 4:34 PM, pravin shelar <pshelar@....org> wrote:
> 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.

Even if the code will change in the future, it seems like an
incremental improvement that will help in some cases so I don't see
much reason to not do this part now.