Re: [dpdk-dev] [PATCH v4 1/4] ethdev: add the API for getting burst mode information

["Wang, Haiyue" <haiyue.wang@intel.com>]

> -----Original Message-----
> From: Jerin Jacob <jerinjacobk@gmail.com>
> Sent: Wednesday, October 30, 2019 12:38
> To: Yigit, Ferruh <ferruh.yigit@intel.com>
> Cc: Thomas Monjalon <thomas@monjalon.net>; Wang, Haiyue <haiyue.wang@intel.com>; dpdk-dev
> <dev@dpdk.org>; Ye, Xiaolong <xiaolong.ye@intel.com>; Kinsella, Ray <ray.kinsella@intel.com>;
> Iremonger, Bernard <bernard.iremonger@intel.com>; Sun, Chenmin <chenmin.sun@intel.com>; Andrew
> Rybchenko <arybchenko@solarflare.com>; Slava Ovsiienko <viacheslavo@mellanox.com>; Stephen Hemminger
> <stephen@networkplumber.org>; David Marchand <david.marchand@redhat.com>; Jerin Jacob
> <jerinj@marvell.com>
> Subject: Re: [dpdk-dev] [PATCH v4 1/4] ethdev: add the API for getting burst mode information
> 
> On Tue, Oct 29, 2019 at 10:29 PM Ferruh Yigit <ferruh.yigit@intel.com> wrote:
> >
> > On 10/26/2019 7:58 AM, Jerin Jacob wrote:
> > > On Sat, Oct 26, 2019 at 3:57 AM Thomas Monjalon <thomas@monjalon.net> wrote:
> > >>
> > >> 25/10/2019 18:02, Jerin Jacob:
> > >>> On Fri, Oct 25, 2019 at 9:15 PM Thomas Monjalon <thomas@monjalon.net> wrote:
> > >>>> 25/10/2019 16:08, Ferruh Yigit:
> > >>>>> On 10/25/2019 10:36 AM, Thomas Monjalon wrote:
> > >>>>>> 15/10/2019 09:51, Haiyue Wang:
> > >>>>>>> Some PMDs have more than one RX/TX burst paths, add the ethdev API
> > >>>>>>> that allows an application to retrieve the mode information about
> > >>>>>>> Rx/Tx packet burst such as Scalar or Vector, and Vector technology
> > >>>>>>> like AVX2.
> > >>>>>>
> > >>>>>> I missed this patch. I and Andrew, maintainers of ethdev, were not CC'ed.
> > >>>>>> Ferruh, I would expect to be Cc'ed and/or get a notification before merging.
> > >>>>>
> > >>>>> It has been discussed in the mail list and went through multiple discussions,
> > >>>>> patch is out since the August, +1 to cc all maintainers I missed that part,
> > >>>>> but when the patch is reviewed and there is no objection, why block the merge?
> > >>>>
> > >>>> I'm not saying blocking the merge.
> > >>>> My bad is that I missed the patch and I am asking for help with a notification
> > >>>> in this case. Same for Andrew I guess.
> > >>>> Note: it is merged in master and I am looking to improve this feature.
> > >>>
> > >>>>>>> +/**
> > >>>>>>> + * Ethernet device RX/TX queue packet burst mode information structure.
> > >>>>>>> + * Used to retrieve information about packet burst mode setting.
> > >>>>>>> + */
> > >>>>>>> +struct rte_eth_burst_mode {
> > >>>>>>> +  uint64_t options;
> > >>>>>>> +};
> > >>>>>>
> > >>>>>> Why a struct for an integer?
> > >>>>>
> > >>>>> Again by a request from me, to not need to break the API if we need to add more
> > >>>>> thing in the future.
> > >>>>
> > >>>> I would replace it with a string. This is the most flexible API.
> > >>>
> > >>> IMO, Probably, best of both worlds make a good option here,
> > >>> as Haiyue suggested if we have an additional dev_specific[1] in structure.
> > >>> and when a pass to the application, let common code make final string as
> > >>> (options flags to string + dev_specific)
> > >>>
> > >>> options flag can be zero if PMD does not have any generic flags nor
> > >>> interested in such a scheme.
> > >>> Generic flags will help at least to have some common code.
> > >>>
> > >>> [1]
> > >>> struct rte_eth_burst_mode {
> > >>>         uint64_t options;
> > >>>         char dev_specific[128]; /* PMD has specific burst mode information */
> > >>> };
> > >>
> > >> I really don't see how we can have generic flags.
> > >> The flags which are proposed are just matching
> > >> the functions implemented in Intel PMDs.
> > >> And this is a complicate solution.
> > >> Why not just returning a name for the selected Rx/Tx mode?
> > >
> > > +1 only for the name
> > >
> > > Let me clarify my earlier proposal:
> > >
> > > 1) The public ethdev API should return only "string" i.e the flags
> > > SHOULD NOT be exposed as ethdev API
> > > i.e
> > > int rte_eth_tx_burst_mode_name(uint16_t port_id, uint16_t queue_id, char *name);
> > >
> > > 2) The PMD interface  to the common code can be following
> > >
> > >  struct eth_pmd_burst_mode {
> > >         uint64_t options;
> > >          char name[128]; /* PMD specific burst mode information */
> > > };
> > >
> > > typedef int (*eth_burst_mode_get_t)(struct rte_eth_dev *dev,
> > >         uint16_t queue_id, struct eth_burst_mode *mode)
> > >
> > > 3) The implementation of rte_eth_tx_burst_mode_name() shall do optons
> > > flag to string converion(again internal to common code implemetation)
> > > and concatenate with eth_pmd_burst_mode::name
> > >
> > > This would help to reuse some of the flags to name conversion logic
> > > across all PMDs.
> > > And PMD are free to return  eth_pmd_burst_mode::options as zero in
> > > that case final
> > > string only be eth_pmd_burst_mode::name.
> > >
> > > I don't see any downside with this approach and it best of both worlds.
> > >
> >
> > I agree it will be hard or restrictive if we want to represent the all data path
> > options with standardized data.
> >
> > But the free text string is good for logging, but not good if the application
> > will get this input and give some decision with it.
> 
> I was thinking it is only for logging. But if the application needs to have
> some decisions with it then below scheme is the best way,
> 
> Though I am not sure, allowing such decision in the application is good or not.
> For instance, If vectorization is AVX512, What kind of decision an
> application can make? If it can make some decision then, will work for
> the NEON case?
> 
> 
> >
> > To combine both two, what do you think a mixed approach, similar to what Jerin
> > described but both options and string is visible to application,
> > and make 'options' only for vectorization information which is limited and be
> > standardized:
> >
> > int rte_eth_tx_burst_mode_get(uint16_t port_id, uint16_t queue_id,
> >         struct rte_eth_burst_mode *mode);
> >
> > struct rte_eth_burst_mode {
> >         uint64_t options; // This is only for VECTORIZATION mode
> >         char *alternate_options;
> > }
> >
> > since "burst_mode:options" only for vectorization, it is limited and can be easy
> > to consume by applications.
> > This means removing some data path options, like "BULK_ALLOC" from current struct.
> 
> ACK
> 
> >
> > 'rte_eth_burst_mode_option_name()' can get "struct rte_eth_burst_mode" as
> > parameter and convert the 'options' to string and combine into single string as
> > a helper function to the applications.
> >
> > And +1 to providing NULL "alternate_options" can return the size of that string.
> 
> ACK
> 
> >
> > And as we find more common/standard data path options, we can move them to the
> > bitfield and remove from the free text. Does it make sense?
> 
> Yes, if, we need to give provide a method to take action for
> application else not.
> 

The new member "char *alternate_options;" is assigned by PMD as static string ?
Like: mode->alternate_options = "abcd" ? Or with fixed array size, so PMD can
format it as needed ?

> >