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

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Date:	Tue, 12 Jan 2016 21:27:12 -0800
From:	pravin shelar <pshelar@....org>
To:	Jesse Gross <jesse@...nel.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 Tue, Jan 12, 2016 at 5:08 PM, Jesse Gross <jesse@...nel.org> wrote:
> On Tue, Jan 12, 2016 at 12:44 PM, pravin shelar <pshelar@....org> wrote:
>> On Tue, Jan 12, 2016 at 11:20 AM, Jesse Gross <jesse@...nel.org> wrote:
>>> 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.
>>
>> I am not sure which cases it help. Can you tell me use cases for
>> internal port in production?
>
> Any traffic coming from the hypervisor itself (as well as tunnels
> although unless you are doing double encapsulation then this patch
> doesn't matter in that case).
>

ok, But majority of traffic comes from VM. So IMO only this patch
would not make much difference.

> Since we're in the merge window now, maybe it makes sense to just go
> for the full version in the next cycle in any case.

ok.