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From: Nithin Dabilpuram <ndabilpuram@marvell.com>
To: Thomas Monjalon <thomas@monjalon.net>
Cc: Jerin Jacob <jerinjacobk@gmail.com>,
	Olivier Matz <olivier.matz@6wind.com>,
	Nithin Dabilpuram <nithind1988@gmail.com>,
	Ferruh Yigit <ferruh.yigit@intel.com>,
	Andrew Rybchenko <arybchenko@solarflare.com>,
	Ori Kam <orika@mellanox.com>,
	Cristian Dumitrescu <cristian.dumitrescu@intel.com>,
	Anatoly Burakov <anatoly.burakov@intel.com>,
	John McNamara <john.mcnamara@intel.com>,
	Marko Kovacevic <marko.kovacevic@intel.com>,
	dpdk-dev <dev@dpdk.org>, Jerin Jacob <jerinj@marvell.com>,
	Krzysztof Kanas <kkanas@marvell.com>
Subject: Re: [dpdk-dev] [EXT] Re: [PATCH 1/3] mbuf: add Tx offloads for packet marking
Date: Fri, 15 May 2020 23:37:54 +0530	[thread overview]
Message-ID: <20200515180754.GC9696@outlook.office365.com> (raw)
In-Reply-To: <2370081.kdYZ1jHi8b@thomas>

On Fri, May 15, 2020 at 06:52:23PM +0200, Thomas Monjalon wrote:
> 15/05/2020 18:26, Jerin Jacob:
> > On Fri, May 15, 2020 at 8:40 PM Thomas Monjalon <thomas@monjalon.net> wrote:
> > > 15/05/2020 15:44, Nithin Dabilpuram:
> > > > On Fri, May 15, 2020 at 03:12:59PM +0200, Thomas Monjalon wrote:
> > > > > 15/05/2020 12:08, Nithin Dabilpuram:
> > > > > > On Thu, May 14, 2020 at 10:29:31PM +0200, Olivier Matz wrote:
> > > > > > > I don't see any better approach than having a mbuf flag. However, I'm
> > > > > > > still not fully convinced that a dynamic flag won't do the job. Taking
> > > > > > > 3 additional flags (among 18 remaing) for this feature also means that
> > > > > > > we have 3 flags less for dynamic flags for all applications, even for
> > > > > > > applications that will not use this feature.
> > > > > > >
> > > > > > > Would it be a problem to use a dynamic flag in this case?
> > > > > > Since packet marking feature itself is already part of spec,
> > > > > > if we move the flags to PMD specific dynamic flag, then it creates a confusion.
> > > > > >
> > > > > > It is not the case of a custom feature supported by a specific PMD.
> > > > > > I believe when other PMD's implement packet marking, the same flags will
> > > > > > suffice.
> > > > >
> > > > > A dynamic flag is not necessarily PMD-specific.
> > > > > It is just avoiding consuming bits if the feature is not used by the application.
> > > > > We must move more existing flags and fields to be dynamic.
> > > > >
> > > > > In general, all new flags and fields in mbuf should be dynamic.
> > > > > And a work must be done to move existing stuff to free more space
> > > > > for more dynamic features.
> > > >
> > > > My bad, I thought dynamic flags can only be used for PMD specific thing.
> > > >
> > > > There is however a cost of using dynamic flag which I think should be avoided
> > > > for DPDK spec defined offloads, though it's fine for PMD specific things.
> > > >
> > > > Dynamic offload flags causes application and PMD to use non constant offset
> > > > or shift which are looked up at init, instead of having a constant shift or
> > > > offset. This indirection costs some cycles due to extra loads in fast path.
> > >
> > > Yes there is a cost. We described it quite clearly last year.
> > > The default rule is now to add new flags and fields as dynamic.
> > > In case the rule was not clear, I will send a patch to insert some
> > > notes in the code and the doc.
> > 
> > Yes. Please send a patch to document the rule. That makes life easy
> > for everyone to make a boolean decision.
> 
> Yes, I will work on it.
> 
> > Here is the comment from mbuf: support dynamic fields and flags commit
> > when accepted this patch.
> > 
> > "    The typical use case is a PMD that registers space for an offload
> >     feature, when the application requests to enable this feature.  As
> >     the space in mbuf is limited, the space should only be reserved if it
> >     is going to be used (i.e when the application explicitly asks for it).
> > "
> 
> OK, there is probably a documentation gap.
> 
> > If you are pushing this feature to dynamic mbuf filed then rte_tm
> > subsystem needs to register dynamic field
> > not the PMD as the feature is part of rte_tm spec.
> 
> Is there a function in rte_tm which initializes or configure the feature?
> 
> 
> > > If you disagree with this new rule, you will have to give very good arguments.
> > 
> > What would the definition of a good argument? as the same logic can be
> > implemented with dynamic vs
> > static at the cost of dynamic indirection.
> 
> I think the only exception to add a static flag or field is to demonstrate
> how basic is the feature.
> But I think all basic features are already integrated for years.
>

Vector implementations will always have huge cost due to dynamic offload
flags. Ofcourse, I don't have a vector implementation for packet marking but,
in future if there is such an offload flag with vector implementation
then hard enforcement will not work.

> 

  parent reply	other threads:[~2020-05-15 18:08 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
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 [this message]
2023-07-31 12:54 ` [dpdk-dev] " Thomas Monjalon
2023-08-14  8:11   ` Nithin Dabilpuram

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