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From: Thomas Monjalon <thomas@monjalon.net>
To: Nithin Dabilpuram <ndabilpuram@marvell.com>
Cc: dev@dpdk.org, "Ananyev,
	Konstantin" <konstantin.ananyev@intel.com>,
	Jerin Jacob <jerinjacobk@gmail.com>,
	"Dumitrescu, Cristian" <cristian.dumitrescu@intel.com>,
	Nithin Dabilpuram <nithind1988@gmail.com>,
	"Yigit, Ferruh" <ferruh.yigit@intel.com>,
	Andrew Rybchenko <arybchenko@solarflare.com>,
	Ori Kam <orika@mellanox.com>,
	"Burakov, Anatoly" <anatoly.burakov@intel.com>,
	"Mcnamara, John" <john.mcnamara@intel.com>,
	"Kovacevic, Marko" <marko.kovacevic@intel.com>,
	dpdk-dev <dev@dpdk.org>, Jerin Jacob <jerinj@marvell.com>,
	Krzysztof Kanas <kkanas@marvell.com>,
	"techboard@dpdk.org" <techboard@dpdk.org>,
	Olivier Matz <olivier.matz@6wind.com>
Subject: Re: [dpdk-dev] [EXT] Re: [PATCH 1/3] mbuf: add Tx offloads for packet marking
Date: Wed, 03 Jun 2020 16:56:08 +0200	[thread overview]
Message-ID: <1634872.Uel37ra6X5@thomas> (raw)
In-Reply-To: <20200603113822.GI12564@platinum>

03/06/2020 13:38, Olivier Matz:
> On Wed, Jun 03, 2020 at 04:14:14PM +0530, Nithin Dabilpuram wrote:
> > On Wed, Jun 03, 2020 at 10:28:44AM +0200, Olivier Matz wrote:
> > > On Tue, Jun 02, 2020 at 07:55:37PM +0530, Nithin Dabilpuram wrote:
> > > > On Tue, Jun 02, 2020 at 10:53:08AM +0000, Ananyev, Konstantin wrote:
> > > > > > > > > I also share Olivier's concern about consuming 3 bits in ol_flags for that feature.
> > > > > > > > > Can it probably be squeezed somehow?
> > > > > > > > > Let say we reserve one flag that this information is present or not, and
> > > > > > > > > re-use one of rx-only fields for store additional information (packet_type, or so).
> > > > > > > > > Or might be some other approach.
> > > > > > > >
> > > > > > > > We are fine with this approach where we define one bit in Tx offloads for pkt
> > > > > > > > marking and and 3 bits reused from Rx offload flags area.
[...]
> > > I'm not a big fan of reusing Rx fields or flags for Tx.
> > > It's not obvious for an application than adding a tx_mark will overwrite
> > > the packet_type. I understand that the risk is limited because packet_type
> > > is Rx and the marks are Tx, but there is still one.

Mixing Rx and Tx info in the same field is a bad design pattern
which will create a lot of difficult bugs.


> > I'm also not a big fan but just wanted to take this approach so that,
> > it can both conserve space and also help fast path.
> > Reusing Rx area is however not a new thing as is already followed for
> > mbuf->txadapter field.

Yes there is a txadapter field union'ed with flow director and QoS.
This is a bad pattern that I highlighted in this presentation (slide 8):
https://www.dpdk.org/wp-content/uploads/sites/35/2019/10/DynamicMbuf.pdf

> Yes, and in my opinion this is something we should avoid when possible,
> because it makes some features exclusive (ex: the big union with
> sched/rss/adapter/usr/...).

Yes, the "RSS union" must be cleaned-up, as some other mbuf parts.


> > Apart from documentation issue, Is there any other issue or future 
> > ramification with using Rx field's for Tx ?
> 
> No, I don't see any other issue except the ones we already mentioned
> (doc, code clarity, ).

"doc clarity" should be understood as the opposite of
"design leading inevitably to bugs".

> > If it is only about documentation, then we can add more documentation to make things clear.

More documentation won't make a bad design better, unfortunately.


> > > To summarize the different proposed approaches (please correct me if I'm wrong):
> > > 
> > > a- add 3 Tx mbuf flags
> > >    (-) consumes limited resource
> > > 
> > > b- add 3 dynamic flags
> > >    (-) slower
> > 
> > - Tx burst Vector implementation can't be done for this tx offload as
> >   offset keeps changing.
> 
> A vector implementation can be done. But yes, it would be slower than
> with a static flag.
> 
> > > c- add 1 Tx flag and union with Rx field
> > >    (-) exclusive with Rx field
> > >    (-) still consumes one flag
> > > 
> > > My preference is still b-, for these reasons:

Me too, my preference is (b).



  parent reply	other threads:[~2020-06-03 14:56 UTC|newest]

Thread overview: 36+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-04-17  7:22 [dpdk-dev] " Nithin Dabilpuram
2020-04-17  7:22 ` [dpdk-dev] [PATCH 2/3] net/octeontx2: add tm packet marking cb Nithin Dabilpuram
2020-04-17  7:22 ` [dpdk-dev] [PATCH 3/3] net/octeontx2: add Tx packet marking offload support Nithin Dabilpuram
2020-05-01 11:18 ` [dpdk-dev] [PATCH 1/3] mbuf: add Tx offloads for packet marking Jerin Jacob
2020-05-04  8:06   ` Olivier Matz
2020-05-04  8:27     ` [dpdk-dev] [EXT] " Nithin Dabilpuram
2020-05-04  9:16       ` Olivier Matz
2020-05-04 10:04         ` Nithin Dabilpuram
2020-05-04 12:27           ` Olivier Matz
2020-05-05  6:19             ` Nithin Dabilpuram
2020-05-13 12:28               ` Nithin Dabilpuram
2020-05-14 20:29               ` Olivier Matz
2020-05-15 10:08                 ` Nithin Dabilpuram
2020-05-15 10:30                   ` Ananyev, Konstantin
2020-05-15 13:57                     ` Nithin Dabilpuram
2020-05-28 15:43                       ` Nithin Dabilpuram
2020-05-30 15:12                         ` Jerin Jacob
2020-06-02 10:53                           ` Ananyev, Konstantin
2020-06-02 14:25                             ` Nithin Dabilpuram
2020-06-03  8:28                               ` Olivier Matz
2020-06-03 10:44                                 ` Nithin Dabilpuram
2020-06-03 11:38                                   ` Olivier Matz
2020-06-03 12:52                                     ` Nithin Dabilpuram
2020-06-03 16:14                                       ` Slava Ovsiienko
2020-06-08  9:39                                         ` Nithin Dabilpuram
2020-06-03 14:56                                     ` Thomas Monjalon [this message]
2020-06-03 10:31                               ` Ananyev, Konstantin
2020-05-15 13:12                   ` Thomas Monjalon
2020-05-15 13:44                     ` Nithin Dabilpuram
2020-05-15 15:10                       ` Thomas Monjalon
2020-05-15 16:26                         ` Jerin Jacob
2020-05-15 16:52                           ` Thomas Monjalon
2020-05-15 17:00                             ` Jerin Jacob
2020-05-15 18:07                             ` Nithin Dabilpuram
2023-07-31 12:54 ` [dpdk-dev] " Thomas Monjalon
2023-08-14  8:11   ` Nithin Dabilpuram

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