Re: [dpdk-dev] [PATCH v2] doc: announce ABI change for rte_eth_dev structure

[Jerin Jacob <jerin.jacob@caviumnetworks.com>]

On Wed, Jul 27, 2016 at 05:33:01PM +0000, Ananyev, Konstantin wrote:
> 
> 
> > -----Original Message-----
> > From: Jerin Jacob [mailto:jerin.jacob@caviumnetworks.com]
> > Sent: Wednesday, July 27, 2016 6:11 PM
> > To: Thomas Monjalon <thomas.monjalon@6wind.com>
> > Cc: Kulasek, TomaszX <tomaszx.kulasek@intel.com>; dev@dpdk.org; Ananyev, Konstantin <konstantin.ananyev@intel.com>
> > Subject: Re: [dpdk-dev] [PATCH v2] doc: announce ABI change for rte_eth_dev structure
> > 
> > On Wed, Jul 27, 2016 at 01:59:01AM -0700, Thomas Monjalon wrote:
> > > > > Signed-off-by: Tomasz Kulasek <tomaszx.kulasek@intel.com>
> > > > > ---
> > > > > +* In 16.11 ABI changes are plained: the ``rte_eth_dev`` structure
> > > > > +will be
> > > > > +  extended with new function pointer ``tx_pkt_prep`` allowing
> > > > > +verification
> > > > > +  and processing of packet burst to meet HW specific requirements
> > > > > +before
> > > > > +  transmit. Also new fields will be added to the ``rte_eth_desc_lim`` structure:
> > > > > +  ``nb_seg_max`` and ``nb_mtu_seg_max`` provideing information
> > > > > +about number of
> > > > > +  segments limit to be transmitted by device for TSO/non-TSO packets.
> > > >
> > > > Acked-by: Konstantin Ananyev <konstantin.ananyev@intel.com>
> > >
> > > I think I understand you want to split the TX processing:
> > > 	1/ modify/write in mbufs
> > > 	2/ write in HW
> > > and let application decide:
> > > 	- where the TX prep is done (which core)
> > 
> > In what basics applications knows when and where to call tx_pkt_prep in fast path.
> > if all the time it needs to call before tx_burst then the PMD won't have/don't need this callback waste cycles in fast path.Is this the expected
> > behavior ?
> > Anything think it as compile time to make other PMDs wont suffer because of this change.
> 
> Not sure what suffering you are talking about...
> Current model - i.e. when application does preparations (or doesn't if none is required)
> on its own and just call tx_burst() would still be there.
> If the app doesn't want to use tx_prep() by some reason - that still ok,
> and decision is up to the particular app. 

So my question is in what basics application decides to call the preparation.
Can you tell me the use case in application perspective?
and what if the PMD does not implement that callback then it is of waste
cycles. Right?

Jerin


> Konstantin
> 
> > 
> > 
> > > 	- what to do if the TX prep fail
> > > So adding some processing in this first part becomes "not too
> > > expensive" or "manageable" from the application point of view.
> > >
> > > If I well understand the intent,
> > >
> > > Acked-by: Thomas Monjalon <thomas.monjalon@6wind.com> (except typos ;)