netdev - Re: [patch net-next RFC 10/12] openvswitch: add support for datapath hardware offload

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Date:	Thu, 4 Sep 2014 11:31:07 +0200
From:	Jiri Pirko <jiri@...nulli.us>
To:	Simon Horman <simon.horman@...ronome.com>
Cc:	John Fastabend <john.fastabend@...il.com>,
	Thomas Graf <tgraf@...g.ch>,
	Scott Feldman <sfeldma@...ulusnetworks.com>,
	netdev@...r.kernel.org, davem@...emloft.net, nhorman@...driver.com,
	andy@...yhouse.net, dborkman@...hat.com, ogerlitz@...lanox.com,
	jesse@...ira.com, pshelar@...ira.com, azhou@...ira.com,
	ben@...adent.org.uk, stephen@...workplumber.org,
	jeffrey.t.kirsher@...el.com, vyasevic@...hat.com,
	xiyou.wangcong@...il.com, john.r.fastabend@...el.com,
	edumazet@...gle.com, jhs@...atatu.com, f.fainelli@...il.com,
	roopa@...ulusnetworks.com, linville@...driver.com,
	dev@...nvswitch.org, jasowang@...hat.com, ebiederm@...ssion.com,
	nicolas.dichtel@...nd.com, ryazanov.s.a@...il.com,
	buytenh@...tstofly.org, aviadr@...lanox.com, nbd@...nwrt.org,
	alexei.starovoitov@...il.com, Neil.Jerram@...aswitch.com,
	ronye@...lanox.com
Subject: Re: [patch net-next RFC 10/12] openvswitch: add support for datapath
 hardware offload

Thu, Sep 04, 2014 at 11:23:35AM CEST, simon.horman@...ronome.com wrote:
>On Thu, Sep 04, 2014 at 11:09:26AM +0200, Jiri Pirko wrote:
>> Thu, Sep 04, 2014 at 11:03:46AM CEST, simon.horman@...ronome.com wrote:
>> >On Sat, Aug 23, 2014 at 10:09:13AM -0700, John Fastabend wrote:
>> >>On 08/23/2014 07:51 AM, Thomas Graf wrote:
>> >>>On 08/23/14 at 11:24am, Jiri Pirko wrote:
>> >>>>Sat, Aug 23, 2014 at 12:53:34AM CEST, sfeldma@...ulusnetworks.com wrote:
>> >>>>>
>> >>>>>On Aug 22, 2014, at 12:39 PM, John Fastabend <john.fastabend@...il.com> wrote:
>> >
>> >[snip]
>> >
>> >>>>>>- Also there is no programmatic way to learn which flows are
>> >>>>>>   in hardware and which in software. There is a pr_warn but
>> >>>>>>   that doesn't help when interacting with the hardware remotely.
>> >>>>>>   I need some mechanism to dump the set of hardware tables and
>> >>>>>>   the set of software tables.
>> >>>>>
>> >>>>>Agreed, we need a way to annotate which flows are installed hardware.
>> >>>>
>> >>>>Yes, we discussed that already. We need to make OVS daemon hw-offload
>> >>>>aware indicating which flow it want/prefers to be offloaded. This is I
>> >>>>believe easily extentable feature and can be added whenever the right
>> >>>>time is.
>> >>>
>> >>>I think the swdev flow API is good as-is. The bitmask specyfing the
>> >>>offload preference with all the granularity (offload-or-fail,
>> >>>try-to-offload, never-offload) needed can be added later, either in
>> >>>OVS only or in swdev itself.
>> >>>
>> >>>What is unclear in this patch is how OVS user space can know which
>> >>>flows are offloaded and which aren't. A status field would help here
>> >>>which indicates either: flow inserted and offloaded, flow inserted but
>> >>>not offloaded. Given that, the API consumer can easily keep track of
>> >>>which flows are currently offloaded.
>> >>>
>> >>
>> >>Right. I think this is basically what Jiri and I discussed when he
>> >>originally posted the series. For my use cases this is one of the
>> >>more interesting pieces. If no one else is looking at it I can try
>> >>it on some of the already existing open source drivers that have some
>> >>very simple support for ingress flow tables read flow director.
>> >
>> >While I agree that it would be good to have such controls I'd like
>> >to take a small step back as I'm not entirely clear how flow deletion
>> >works in the current code. I am specifically refering to the Open vSwitch
>> >use-case.
>> >
>> >My assumption is that if a flow is offloaded then once it is set up in
>> >hardware packets won't hit the datapath any more.  However, statistics need
>> >to be updated in the datapath for active flows otherwise they will be
>> >evicted by ovs-vswtichd.
>> 
>> Yes, that is exactly what happens.
>> 
>> >
>> >In short, I was expecting to see get and statistics callbacks.
>> 
>> We plan to implement this in rocker device as one of next steps.
>
>Great. Will that also include some swdev API and datapath modifications?

sure.
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