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From: Simon Horman <simon.horman@corigine.com>
To: Jamal Hadi Salim <jhs@mojatatu.com>
Cc: Vlad Buslov <vladbu@nvidia.com>,
	David Miller <davem@davemloft.net>,
	Jakub Kicinski <kuba@kernel.org>,
	Cong Wang <xiyou.wangcong@gmail.com>,
	Jiri Pirko <jiri@mellanox.com>,
	netdev@vger.kernel.org, oss-drivers@corigine.com,
	Baowen Zheng <baowen.zheng@corigine.com>,
	Louis Peens <louis.peens@corigine.com>,
	Ido Schimmel <idosch@nvidia.com>, Jiri Pirko <jiri@resnulli.us>,
	Roopa Prabhu <roopa@nvidia.com>
Subject: Re: [PATCH net-next 1/3] flow_offload: allow user to offload tc action to net device
Date: Fri, 30 Jul 2021 15:20:02 +0200	[thread overview]
Message-ID: <20210730132002.GA31790@corigine.com> (raw)
In-Reply-To: <2ba4e24f-e34e-f893-d42b-d0fd40794da5@mojatatu.com>

On Fri, Jul 30, 2021 at 06:17:18AM -0400, Jamal Hadi Salim wrote:
> On 2021-07-28 10:46 a.m., Simon Horman wrote:
> > On Wed, Jul 28, 2021 at 09:51:00AM -0400, Jamal Hadi Salim wrote:
> > > On 2021-07-28 3:46 a.m., Simon Horman wrote:
> > > > On Tue, Jul 27, 2021 at 07:47:43PM +0300, Vlad Buslov wrote:
> > > > > On Tue 27 Jul 2021 at 19:13, Jamal Hadi Salim <jhs@mojatatu.com> wrote:
> > > > > > On 2021-07-27 10:38 a.m., Vlad Buslov wrote:
> > > > > > > On Tue 27 Jul 2021 at 16:04, Simon Horman <simon.horman@corigine.com> wrote:
> > > 
> > > [..]
> > > 
> > > > > > > I think we have the same issue with filters - they might not be in
> > > > > > > hardware after driver callback returned "success" (due to neigh state
> > > > > > > being invalid for tunnel_key encap, for example).
> > > > > > 
> > > > > > Sounds like we need another state for this. Otherwise, how do you debug
> > > > > > that something is sitting in the driver and not in hardware after you
> > > > > > issued a command to offload it? How do i tell today?
> > > > > > Also knowing reason why something is sitting in the driver would be
> > > > > > helpful.
> > > > > 
> > > > > It is not about just adding another state. The issue is that there is no
> > > > > way for drivers to change the state of software filter dynamically.
> > > > 
> > > > I think it might be worth considering enhancing things at some point.
> > > > But I agree that its more than a matter of adding an extra flag. And
> > > > I think it's reasonable to implement something similar to the classifier
> > > > current offload handling of IN_HW now and consider enhancements separately.
> > > 
> > > Debugability is very important. If we have such gotchas we need to have
> > > the admin at least be able to tell if the driver returns "success"
> > > and the request is still sitting in the driver for whatever reason
> > > At minimal there needs to be some indicator somewhere which say
> > > "inprogress" or "waiting for resolution" etc.
> > > If the control plane(user space app) starts making other decisions
> > > based on assumptions that filter was successfully installed i.e
> > > packets are being treated in the hardware then there could be
> > > consequences when this assumption is wrong.
> > > 
> > > So if i undestood the challenge correctly it is: how do you relay
> > > this info back so it is reflected in the filter details. Yes that
> > > would require some mechanism to exist and possibly mapping state
> > > between whats in the driver and in the cls layer.
> > > If i am not mistaken, the switchdev folks handle this asynchronicty?
> > > +Cc Ido, Jiri, Roopa
> > > 
> > > And it should be noted that: Yes, the filters have this
> > > pre-existing condition but doesnt mean given the opportunity
> > > to do actions we should replicate what they do.
> > 
> > I'd prefer symmetry between the use of IN_HW for filters and actions,
> > which I believe is what Vlad has suggested.
> 
> It still not clear to me what it means from a command line pov.
> How do i add a rule and when i dump it what does it show?

How about we confirm that once we've implemented the feature.

But I would assume that:

* Existing methods for adding rules work as before
* When one dumps an action (in a sufficiently verbose
  way) the in_hw and in_hw_counter fields are displayed as they are for
  filters.

Does that help?

> > If we wish to enhance things - f.e. for debugging, which I
> > agree is important - then I think that is a separate topic.
> > 
> 
> My only concern is not to repeat mistakes that are in filters
> just for the sake of symmetry. Example the fact that something
> went wrong with insertion or insertion is still in progress
> and you get an indication that all went well.
> Looking at mlnx (NIC) ndrivers it does seem that in the normal case
> the insertion into hw is synchronous (for anything that is not sw
> only). I didnt quiet see what Vlad was referring to.
> We have spent literally hours debugging issues where rules are being
> offloaded thinking it was the driver so any extra info helps.

I do think there is a value to symmetry between the APIs.
And I don't think doing so moves things in a bad direction.
But rather a separate discussion is needed to discuss how to
improve debuggability.

...

> > > > > > I was looking at it more as a (currently missing) feature improvement.
> > > > > > We already have a use case that is implemented by s/w today. The feature
> > > > > > mimics it in h/w.
> > > > > > 
> > > > > > At minimal all existing NICs should be able to support the counters
> > > > > > as mapped to simple actions like drop. I understand for example if some
> > > > > > cant support adding separately offloading of tunnels for example.
> > > > > > So the syntax is something along the lines of:
> > > > > > 
> > > > > > tc actions add action drop index 15 skip_sw
> > > > > > tc filter add dev ...parent ... protocol ip prio X ..\
> > > > > > u32/flower skip_sw match ... flowid 1:10 action gact index 15
> > > > > > 
> > > > > > You get an error if counter index 15 is not offloaded or
> > > > > > if skip_sw was left out..
> > > > > > 
> > > > > > And then later on, if you support sharing of actions:
> > > > > > tc filter add dev ...parent ... protocol ip prio X2 ..\
> > > > > > u32/flower skip_sw match ... flowid 1:10 action gact index 15
> > > > 
> > > > Right, I understand that makes sense and is internally consistent.
> > > > But I think that in practice it only makes a difference "Approach B"
> > > > implementations, none of which currently exist.
> > > > 
> > > 
> > > At minimal:
> > > Shouldnt counters (easily correlated to basic actions like drop or
> > > accept) fit the scenario of:
> > > tc actions add action drop index 15 skip_sw
> > > tc filter add dev ...parent ... protocol ip prio X .. \
> > > u32/flower skip_sw match ... flowid 1:10 action gact index 15
> > > 
> > > ?
> > > 
> > > > I would suggest we can add this when the need arises, rather than
> > > > speculatively without hw/driver support. Its not precluded by the current
> > > > model AFAIK.
> > > > 
> > > 
> > > We are going to work on a driver that would have the "B" approach.
> > > I am hoping - whatever the consensus here - it doesnt require a
> > > surgery afterwards to make that work.
> > 
> > You should be able to build on the work proposed here to add what you
> > suggest into the framework to meet these requirements for your driver work.
> > 
> 
> Then we are good. These are the same patches you have here?

Yes.

  parent reply	other threads:[~2021-07-30 13:20 UTC|newest]

Thread overview: 42+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-22  9:19 [PATCH net-next 0/3] flow_offload: hardware offload of TC actions Simon Horman
2021-07-22  9:19 ` [PATCH net-next 1/3] flow_offload: allow user to offload tc action to net device Simon Horman
2021-07-22 12:24   ` Roi Dayan
2021-07-22 13:19     ` Simon Horman
2021-07-22 13:29   ` Vlad Buslov
2021-07-22 13:33     ` Jamal Hadi Salim
2021-07-27 13:04       ` Simon Horman
2021-07-27 14:38         ` Vlad Buslov
2021-07-27 16:13           ` Jamal Hadi Salim
2021-07-27 16:47             ` Vlad Buslov
2021-07-28  7:46               ` Simon Horman
2021-07-28  8:05                 ` Vlad Buslov
2021-07-28 13:51                 ` Jamal Hadi Salim
2021-07-28 14:46                   ` Simon Horman
2021-07-30 10:17                     ` Jamal Hadi Salim
2021-07-30 11:40                       ` Vlad Buslov
2021-08-03  9:57                         ` Jamal Hadi Salim
2021-08-03 12:02                           ` tc offload debug-ability Jamal Hadi Salim
2021-08-03 12:14                             ` Vlad Buslov
2021-08-03 12:50                               ` Jamal Hadi Salim
2021-08-03 13:34                                 ` Ido Schimmel
2021-07-30 13:20                       ` Simon Horman [this message]
2021-08-03 10:14                         ` [PATCH net-next 1/3] flow_offload: allow user to offload tc action to net device Jamal Hadi Salim
2021-08-03 11:36                           ` Simon Horman
2021-08-03 11:45                             ` Jamal Hadi Salim
2021-08-03 12:31                               ` Simon Horman
2021-08-03 13:01                                 ` Jamal Hadi Salim
2021-08-03 14:46                                   ` Simon Horman
2021-07-22 13:57   ` kernel test robot
2021-07-22 15:31   ` kernel test robot
2021-08-03 10:50   ` Jamal Hadi Salim
2021-08-03 11:05   ` Jamal Hadi Salim
2021-08-03 11:31     ` Simon Horman
2021-07-22  9:19 ` [PATCH net-next 2/3] flow_offload: add process to delete offloaded actions from " Simon Horman
2021-07-22 14:25   ` Vlad Buslov
2021-07-22 14:50   ` kernel test robot
2021-07-22 17:07   ` kernel test robot
2021-08-03 10:59   ` Jamal Hadi Salim
2021-07-22  9:19 ` [PATCH net-next 3/3] flow_offload: add process to update action stats from hardware Simon Horman
2021-07-22 14:55   ` Vlad Buslov
2021-08-03 11:24   ` Jamal Hadi Salim
2021-08-03 11:35     ` Simon Horman

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