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: Yigit, Ferruh <ferruh.yigit@intel.com>
> Sent: Wednesday, October 30, 2019 00:59
> To: Jerin Jacob <jerinjacobk@gmail.com>; Thomas Monjalon <thomas@monjalon.net>
> Cc: 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 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.
> 
> 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.
> 
> '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.
> 

Change:
const char *
rte_eth_burst_mode_option_name(uint64_t option)

to:
int
rte_eth_burst_mode_option_name(struct rte_eth_burst_mode *mode, char *str) ?
If str == NULL, return the length of 'mode->options' ?


> And +1 to providing NULL "alternate_options" can return the size of that string.
> 

struct rte_eth_burst_mode mode;

mode.alternate_options = NULL
rte_eth_tx_burst_mode_get(0, 0, &mode) return the length of 'mode.alternate_options' ?
If so, it means that every PMD need to handle this, right ?

> 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?