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

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

Hi Jerin,

> -----Original Message-----
> From: Jerin Jacob <jerinjacobk@gmail.com>
> Sent: Tuesday, October 29, 2019 16:35
> To: Wang, Haiyue <haiyue.wang@intel.com>
> Cc: Thomas Monjalon <thomas@monjalon.net>; Yigit, Ferruh <ferruh.yigit@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
> 
> > > > > > > 1) We can not standardize all flags when it comes to HW specific
> > > > > > > details. We should NOT pollute public API with HW specific details.
> > > > > >
> > > > > > Currently, no detail to HW NIC specific.
> > > > >
> > > > > Yes. What if I want to add a "String" they represent a specific mode of PMD,
> > > > > so that I know what mode PMD really runs.
> > > > > It is not worth adding a flag for that in public API for HW specific notion.
> > > > > That's the problem.
> > > > >
> > > > > >
> > > > > > > 2) There is a danger if application starts taking any action based on
> > > > > > > flags. It should be only for display purpose so in that case public
> > > > > > > API should be the string to avoid misuse of the API(eventually the app
> > > > > > > will fail on some PMD
> > > > > > > if it takes any action based on the flag)
> > > > > >
> > > > > > These flags are *read only* for information. Can't image how to hack DPDK. ;-)
> > > > >
> > > > > To clarify:
> > > > > If we expose flag say RTE_ETH_BURST_SIMPLE then the application can take
> > > > > some action based on
> > > > > if (flag == RTE_ETH_BURST_SIMPLE)
> > > > >     do_some_thing();
> > > > >
> > > > > If the purpose is ONLY for "display" as info then exposing as the string will
> > > > > enable to NOT standardize i.e application can never check based on
> > > > > the string name(as it is not standardized) hence no danger.
> > > > >
> > > > > So what is the purpose of this API? Just display or are you expecting
> > > > > the application can do any action based on this?
> > > >
> > > > Oh, I see. Mainly for showing which burst rx/tx module running:
> > >
> > > If so, the public API should be as string to avoid any other interpreation of
> > > flags in application.
> > >
> > > And it makes application life easy too.
> > >
> > >
> >
> > At first, we do use string, but string contains same words. Off course, this
> > is from CPU's view. Our two PMDs string are nearly the same, so we use bit
> > instead. And people may check which CPU's vertor using. And we provide to_string
> > to help make both happy. Not sure we really make them happy.
> 
> # I understand the flags can enable us to reuse some of the code and I
> agree with that.
> But it has the downside mentioned above.
> 
> How about the following to have the best of both worlds.
> 
> 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);
> 

How about *_str_* style ?

int
rte_eth_rx_burst_mode_str_get(uint16_t port_id, uint16_t queue_id,
			  	      char *buf, int buflen)


> 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 */
> };
> 

struct eth_pmd_burst_mode {
	uint64_t options;
	char dev_specific[128]; /* PMD specific burst mode information */
};

Still use 'dev_specific' ? Since whole structure 'struct eth_pmd_burst_mode'
will be translated into string name.

> 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
> 

Should be better to use the user input buffer w/ size ? Since now 'option'
is private to PMD.

int
rte_eth_rx_burst_mode_str_get(uint16_t port_id, uint16_t queue_id,
			  	      char *buf, int buflen)

And the concatenate format : "options string, dev_specific"
                                            ^
                                            If option is non-zero, and has device specific, add this ','
                                            as separation ?

> 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.
> 
> 
> >
> > > >
> > > > https://docs.fd.io/vpp/18.11/d7/d1d/plugins_2dpdk_2device_2format_8c_source.html
> > > >
> > > > s = format (s, "%Utx burst function: %s\n",
> > > >   579                   format_white_space, indent + 2,
> > > >   580                   ptr2sname (rte_eth_devices[xd->port_id].tx_pkt_burst));
> > > >   581       s = format (s, "%Urx burst function: %s\n",
> > > >   582                   format_white_space, indent + 2,
> > > >   583                   ptr2sname (rte_eth_devices[xd->port_id].rx_pkt_burst));
> > > >
> > > > https://docs.fd.io/vpp/18.11/d7/d1d/plugins_2dpdk_2device_2format_8c_source.html
> > > >
> > > > 488 static const char *
> > > >   489 ptr2sname (void *p)
> > > >   490 {
> > > >   491   Dl_info info = { 0 };
> > > >   492
> > > >   493   if (dladdr (p, &info) == 0)
> > > >   494     return 0;
> > > >   495
> > > >   496   return info.dli_sname;
> > > >   497 }
> > > >
> > > >     tx burst function: ixgbe_xmit_pkts
> > > >     rx burst function: ixgbe_recv_pkts
> > > >
> > > > If the PMD's rx/tx is *static* function, 'ptr2name' returns 'nil'.