[dpdk-dev] [PATCH v8 02/19] eal: enable multi process init callback

[Zhang, Qi Z]

> -----Original Message-----
> From: Thomas Monjalon [mailto:thomas at monjalon.net]
> Sent: Wednesday, July 4, 2018 5:51 AM
> To: Zhang, Qi Z <qi.z.zhang at intel.com>
> Cc: dev at dpdk.org; Burakov, Anatoly <anatoly.burakov at intel.com>; Ananyev,
> Konstantin <konstantin.ananyev at intel.com>; Richardson, Bruce
> <bruce.richardson at intel.com>; Yigit, Ferruh <ferruh.yigit at intel.com>; Shelton,
> Benjamin H <benjamin.h.shelton at intel.com>; Vangati, Narender
> <narender.vangati at intel.com>
> Subject: Re: [dpdk-dev] [PATCH v8 02/19] eal: enable multi process init callback
> 
> 03/07/2018 17:16, Zhang, Qi Z:
> > From: Thomas Monjalon [mailto:thomas at monjalon.net]
> > >
> > > Hi Qi,
> > >
> > > Sorry I do not understand neither the commit log, nor the doxygen.
> > > If it can help, consider your reader is in a bad mood and needs a
> > > pleasant description.
> >
> > OK, I think is not a grammar issue since it almost passed a grammar
> > check :)
> >
> > So more explanation:
> > Basically we need to register mp action callback in ethdev layer,
> 
> What is "mp action callback"?

rte_mp_action_register(ETH_DEV_MP_ACTION_REQUEST, handle_secondary_request);

in this case ETH_DEV_MP_ACTION_REQUEST is the action,
and handle_secondary_request is the callback which will be invoked when the action received from another process.

> Why do you need it in ethdev?

Based on current implementation, IPC is required during dev_attach/dev_detach.
so we need to make sure callback is registered before that happen.

> 
> > but this should happens during rte_eal_init
> 
> Why it should be done in rte_eal_init?
Either we can expose an ethdev API like rte_eth_dev_mp_init, to let application do this explicitly, or we can let application assume all necessary callback has been registered when DPDK is initialized. (rte_eal_init)
> 
> > ethdev don't have a general init function that can be invoked by eal
> > during rte_eal_init, actually I guess, all no-eal module don't have
> 
> What is "no-eal module"?

A module like lib_ethdev which lib_eal should not depend on.

> 
> > in vdev bus, it register the mp action at the first bus scan happen.
> > but in ethdev, we can't do that way, because, we don' t know when
> > device will be attached or detached.
> > so we need that function to help register a callback function which will be
> invoked during rte_eal_init.
> >
> >
> > >
> > > 02/07/2018 07:44, Qi Zhang:
> > > > Introduce new API rte_eal_register_mp_init that help to register a
> > > > callback function which will be invoked right after multi-process
> > > > channel be established (rte_mp_channel_init). Typically the API
> > > > will be used by other module that want it's mp channel action
> > > > callbacks can be registered during rte_eal_init automatically.
> > > [...]
> > > > +/**
> > > > + * @warning
> > > > + * @b EXPERIMENTAL: this API may change without prior notice
> > > > + *
> > > > + * Register a callback function that will be invoked right after
> > > > + * multi-process channel be established (rte_mp_channel_init).
> > > > +Typically
> > > > + * the function is used by other module that want it's mp channel
> > > > + * action callbacks can be registered during rte_eal_init automatically.
> > > > + *
> > > > + * @note
> > > > + *   This function only take effect when be called before rte_eal_init,
> > > > + *   and all registered callback will be clear during rte_eal_cleanup.
> 
>