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 13:47
> 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 11:12 AM Wang, Haiyue <haiyue.wang@intel.com> wrote:
> >
> > > -----Original Message-----
> > > From: Jerin Jacob <jerinjacobk@gmail.com>
> > > Sent: Tuesday, October 29, 2019 13:20
> > > 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 10:14 AM Wang, Haiyue <haiyue.wang@intel.com> wrote:
> > > >
> > > > > -----Original Message-----
> > > > > From: Jerin Jacob <jerinjacobk@gmail.com>
> > > > > Sent: Tuesday, October 29, 2019 11:38
> > > > > 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
> > > > >
> > > > > > > > > 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.
> > > > > > >
> > > > > >
> > > > > > In fact, 'rte_eth_burst_mode_option_name' for single option, not
> > > > > > for struct eth_pmd_burst_mode::option[s]. Need loop to display them.
> > > > >
> > > > > I see two issues with the flag approach in public API(Internally for
> > > > > common code it fine to avoid code duplication)
> > > > >
> > > > > 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.

> >
> > 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'.