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From: Thomas Monjalon <thomas@monjalon.net>
To: Ivan Malov <ivan.malov@oktetlabs.ru>,
	Ilya Maximets <i.maximets@ovn.org>,
	Eli Britstein <elibr@nvidia.com>,
	Andrew Rybchenko <andrew.rybchenko@oktetlabs.ru>
Cc: dev@dpdk.org, Smadar Fuks <smadarf@marvell.com>,
	Hyong Youb Kim <hyonkim@cisco.com>,
	Kishore Padmanabha <kishore.padmanabha@broadcom.com>,
	Ori Kam <orika@nvidia.com>,
	Ajit Khaparde <ajit.khaparde@broadcom.com>,
	Jerin Jacob <jerinj@marvell.com>, John Daley <johndale@cisco.com>,
	Ferruh Yigit <ferruh.yigit@intel.com>
Subject: Re: [dpdk-dev] [RFC PATCH] ethdev: clarify flow action PORT ID semantics
Date: Wed, 02 Jun 2021 14:16:33 +0200	[thread overview]
Message-ID: <4411589.J5AvIlR3Bg@thomas> (raw)
In-Reply-To: <8c4f559e-3430-e2d5-1199-f1d4f4a8546d@ovn.org>

01/06/2021 14:10, Ilya Maximets:
> On 6/1/21 1:14 PM, Ivan Malov wrote:
> > By its very name, action PORT_ID means that packets hit an ethdev with the
> > given DPDK port ID. At least the current comments don't state the opposite.
> > That said, since port representors had been adopted, applications like OvS
> > have been misusing the action. They misread its purpose as sending packets
> > to the opposite end of the "wire" plugged to the given ethdev, for example,
> > redirecting packets to the VF itself rather than to its representor ethdev.
> > Another example: OvS relies on this action with the admin PF's ethdev port
> > ID specified in it in order to send offloaded packets to the physical port.
> > 
> > Since there might be applications which use this action in its valid sense,
> > one can't just change the documentation to greenlight the opposite meaning.
> > This patch adds an explicit bit to the action configuration which will let
> > applications, depending on their needs, leverage the two meanings properly.
> > Applications like OvS, as well as PMDs, will have to be corrected when the
> > patch has been applied. But the improved clarity of the action is worth it.
> > 
> > The proposed change is not the only option. One could avoid changes in OvS
> > and PMDs if the new configuration field had the opposite meaning, with the
> > action itself meaning delivery to the represented port and not to DPDK one.
> > Alternatively, one could define a brand new action with the said behaviour.
> 
> We had already very similar discussions regarding the understanding of what
> the representor really is from the DPDK API's point of view, and the last
> time, IIUC, it was concluded by a tech. board that representor should be
> a "ghost of a VF", i.e. DPDK APIs should apply configuration by default to
> VF and not to the representor device:
>   https://patches.dpdk.org/project/dpdk/cover/20191029185051.32203-1-thomas@monjalon.net/#104376
> This wasn't enforced though, IIUC, for existing code and semantics is still mixed.

Quoting myself from above link:
"the representor port must be a real DPDK port, not a ghost."
and
"During the Technical Board yesterday, it was decided to go with Intel
understanding of what is a representor, i.e. a ghost of the VF."
and
"we will continue to mix VF and representor operations
with the same port ID. For the record, I believe it is very bad."

> I still think that configuration should be applied to VF, and the same applies
> to rte_flow API.  IMHO, average application should not care if device is
> a VF itself or its representor.  Everything should work exactly the same.

What means "work exactly the same"?
Is it considering what is behind the representor silently,
or considering the representor as a real port?

There is a need to really consider representor port as any other port,
and stop this ugly mix. I want to propose such change again for DPDK 21.11.
To me the real solution is to use a bit in the port id of a representor
for explicitly identifying the port behind the representor.
This bit could be translated as a flag or a sign in testpmd text grammar.

> I think this matches with the original idea/design of the switchdev functionality
> in the linux kernel and also matches with how the average user thinks about
> representor devices.

There is no "average" user or application, just right and wrong.
In the switchdev model, a representor is a port of a switch like
any other port, not a ghost of its peer.

> If some specific use-case requires to distinguish VF from the representor,
> there should probably be a separate special API/flag for that.

Yes, port ID of a representor must be the representor itself,
and a bit can help reaching the port behind the representor.




  parent reply	other threads:[~2021-06-02 12:16 UTC|newest]

Thread overview: 40+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-06-01 11:14 Ivan Malov
2021-06-01 12:10 ` Ilya Maximets
2021-06-01 13:24   ` Eli Britstein
2021-06-01 14:35     ` Andrew Rybchenko
2021-06-01 14:44       ` Eli Britstein
2021-06-01 14:50         ` Ivan Malov
2021-06-01 14:53         ` Andrew Rybchenko
2021-06-02  9:57           ` Eli Britstein
2021-06-02 10:50             ` Andrew Rybchenko
2021-06-02 11:21               ` Eli Britstein
2021-06-02 11:57                 ` Andrew Rybchenko
2021-06-02 12:36                 ` Ivan Malov
2021-06-03  9:18                   ` Ori Kam
2021-06-03  9:55                     ` Andrew Rybchenko
2021-06-07  8:28                       ` Thomas Monjalon
2021-06-07  9:42                         ` Andrew Rybchenko
2021-06-07 12:08                           ` Ori Kam
2021-06-07 13:21                             ` Ilya Maximets
2021-06-07 16:07                               ` Thomas Monjalon
2021-06-08 16:13                                 ` Thomas Monjalon
2021-06-08 16:32                                   ` Andrew Rybchenko
2021-06-08 18:49                                     ` Thomas Monjalon
2021-06-09 14:31                                       ` Andrew Rybchenko
2021-06-01 14:49     ` Ivan Malov
2021-06-01 14:28   ` Ivan Malov
2021-06-02 12:46     ` Ilya Maximets
2021-06-02 16:26       ` Andrew Rybchenko
2021-06-02 17:35         ` Ilya Maximets
2021-06-02 19:35           ` Ivan Malov
2021-06-03  9:29             ` Ilya Maximets
2021-06-03 10:33               ` Andrew Rybchenko
2021-06-03 11:05                 ` Ilya Maximets
2021-06-03 11:29               ` Ivan Malov
2021-06-07 19:27                 ` Ilya Maximets
2021-06-07 20:39                   ` Ivan Malov
2021-06-25 13:04       ` Ferruh Yigit
2021-06-02 12:16   ` Thomas Monjalon [this message]
2021-06-02 12:53     ` Ilya Maximets
2021-06-02 13:10     ` Andrew Rybchenko
2021-09-03  7:46 ` [dpdk-dev] [PATCH v1] " Andrew Rybchenko

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