RE: [PATCH v2 1/3] eventdev/eth_rx: add params set/get APIs

["Naga Harish K, S V" <s.v.naga.harish.k@intel.com>]

Hi Jerin,

> -----Original Message-----
> From: Jerin Jacob <jerinjacobk@gmail.com>
> Sent: Monday, January 30, 2023 8:13 PM
> To: Naga Harish K, S V <s.v.naga.harish.k@intel.com>
> Cc: jerinj@marvell.com; Carrillo, Erik G <erik.g.carrillo@intel.com>; Gujjar,
> Abhinandan S <abhinandan.gujjar@intel.com>; dev@dpdk.org;
> Jayatheerthan, Jay <jay.jayatheerthan@intel.com>
> Subject: Re: [PATCH v2 1/3] eventdev/eth_rx: add params set/get APIs
> 
> On Mon, Jan 30, 2023 at 3:26 PM Naga Harish K, S V
> <s.v.naga.harish.k@intel.com> wrote:
> >
> >
> >
> > > -----Original Message-----
> > > From: Jerin Jacob <jerinjacobk@gmail.com>
> > > Sent: Saturday, January 28, 2023 4:24 PM
> > > To: Naga Harish K, S V <s.v.naga.harish.k@intel.com>
> > > Cc: jerinj@marvell.com; Carrillo, Erik G
> > > <erik.g.carrillo@intel.com>; Gujjar, Abhinandan S
> > > <abhinandan.gujjar@intel.com>; dev@dpdk.org; Jayatheerthan, Jay
> > > <jay.jayatheerthan@intel.com>
> > > Subject: Re: [PATCH v2 1/3] eventdev/eth_rx: add params set/get APIs
> > >
> > > On Wed, Jan 25, 2023 at 10:02 PM Naga Harish K, S V
> > > <s.v.naga.harish.k@intel.com> wrote:
> > > >
> > > >
> > > >
> > > > > -----Original Message-----
> > > > > From: Jerin Jacob <jerinjacobk@gmail.com>
> > >
> > > > > > > >
> > > > > > > > > > +        */
> > > > > > > > > > +       uint32_t rsvd[15];
> > > > > > > > > > +       /**< Reserved fields for future use */
> > > > > > > > >
> > > > > > > > > Introduce rte_event_eth_rx_adapter_runtime_params_init()
> > > > > > > > > to
> > > > > make
> > > > > > > > > sure rsvd is zero.
> > > > > > > > >
> > > > > > > >
> > > > > > > > The reserved fields are not used by the adapter or application.
> > > > > > > > Not sure Is it necessary to Introduce a new API to clear
> > > > > > > > reserved
> > > fields.
> > > > > > >
> > > > > > > When adapter starts using new fileds(when we add new fieds
> > > > > > > in future), the old applicaiton which is not using
> > > > > > > rte_event_eth_rx_adapter_runtime_params_init() may have
> junk
> > > > > > > value and then adapter implementation will behave bad.
> > > > > > >
> > > > > > >
> > > > > >
> > > > > > does it mean, the application doesn't re-compile for the new DPDK?
> > > > >
> > > > > Yes. No need recompile if ABI not breaking.
> > > > >
> > > > > > When some of the reserved fields are used in the future, the
> > > > > > application
> > > > > also may need to be recompiled along with DPDK right?
> > > > > > As the application also may need to use the newly consumed
> > > > > > reserved
> > > > > fields?
> > > > >
> > > > > The problematic case is:
> > > > >
> > > > > Adapter implementation of 23.07(Assuming there is change params)
> > > > > field needs to work with application of 23.03.
> > > > > rte_event_eth_rx_adapter_runtime_params_init() will sove that.
> > > > >
> > > >
> > > > As rte_event_eth_rx_adapter_runtime_params_init() initializes only
> > > reserved fields to zero,  it may not solve the issue in this case.
> > >
> > > rte_event_eth_rx_adapter_runtime_params_init() needs to zero all
> > > fields, not just reserved field.
> > > The application calling sequence  is
> > >
> > > struct my_config c;
> > > rte_event_eth_rx_adapter_runtime_params_init(&c)
> > > c.interseted_filed_to_be_updated = val;
> > >
> > Can it be done like
> >         struct my_config c = {0};
> >         c.interseted_filed_to_be_updated = val; and update Doxygen
> > comments to recommend above usage to reset all fields?
> > This way,  rte_event_eth_rx_adapter_runtime_params_init() can be
> avoided.
> 
> Better to have a function for documentation clarity. Similar scheme already
> there in DPDK. See rte_eth_cman_config_init()
> 
> 


The reference function rte_eth_cman_config_init() is resetting the params struct and initializing the required params with default values in the pmd cb.
The proposed rte_event_eth_rx_adapter_runtime_params_init () API just needs to reset the params struct. There are no pmd CBs involved.
Having an API just to reset the struct seems overkill. What do you think?

> >
> > > Let me share an example and you can tell where is the issue
> > >
> > > 1)Assume parameter structure is 64B and for 22.03 8B are used.
> > > 2)rte_event_eth_rx_adapter_runtime_params_init() will clear all 64B.
> > > 3)There is an application written based on 22.03 which using only 8B
> > > after calling rte_event_eth_rx_adapter_runtime_params_init()
> > > 4)Assume, in 22.07 another 8B added to structure.
> > > 5)Now, the application (3) needs to run on 22.07. Since the
> > > application is calling
> > > rte_event_eth_rx_adapter_runtime_params_init()
> > > and 9 to 15B are zero, the implementation will not go bad.
> > >
> > > > The old application only tries to set/get previous valid fields
> > > > and the newly
> > > used fields may still contain junk value.
> > > > If the application wants to make use of any the newly used params,
> > > > the
> > > application changes are required anyway.
> > >
> > > Yes. If application wants to make use of newly added features. No
> > > need to change if new features are not needed for old application.