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: Tuesday, October 29, 2019 20:57
> 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
> 
> On Tue, Oct 29, 2019 at 4:56 PM Wang, Haiyue <haiyue.wang@intel.com> wrote:
> >
> > Hi Jerin,
> 
> Hi Wang
> 
> >
> > > -----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 ?
> 
> _name kind of implies it the string. may be _mode is good as it is short.
> 
> > int
> > rte_eth_rx_burst_mode_str_get(uint16_t port_id, uint16_t queue_id,
> >                                       char *buf, int buflen)
> 

About the function, keep the same is better ? Then we need no whole
replace, just update the parameters, and the parameters indicated that
it is in string format.

> We don't need buflen as it is not known to the application. The
> typical pattern, we followed,
> in dpdk is, when function called buf as NULL then the function returns
> the expected size so that
> the application can alloc and get the buffer from ethdev layer on the
> next iteration.
> 
> 

A little complicated and too heavy for using ? where is the example code ?
I found that 'snprintf' had this feature, but 'sprintf' didn't. And we need
to loop all the options, hard to do like: 'buf + len' for next string ?

int main(void)
{
        int len;
        char *buf = NULL;

        len = sprintf(buf, "test %d", 2);

        printf("len = %d\n", len);

        return 0;
}

Segmentation fault (core dumped)

==============

#include <stdio.h>


int main(void)
{
        int len;
        char *buf = NULL;

        len = snprintf(buf, 0, "test %d", 2);

        printf("len = %d\n", len);

        return 0;
}

len = 6

> 
> 
> 
> >
> >
> > > 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.
> 
> Yes.
> options - for generic flags to reuse the code
> dev_specific - for PMD specific 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.
> 
> see above. No need for a separate argument. NULL case it can return
> the expected size.
> 
> > 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 ?
> 
> Looks good to me.
> 
> >
> > > 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'.