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

[Jerin Jacob <jerinjacobk@gmail.com>]

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.






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