Re: [dpdk-dev] [RFC PATCH 4/4] ethdev: add helpers to move to the new offloads API

[Thomas Monjalon <thomas@monjalon.net>]

24/08/2017 09:12, Shahaf Shuler:
> Thursday, August 24, 2017 1:06 AM, Thomas Monjalon:
> > 23/08/2017 15:13, Shahaf Shuler:
> > > Wednesday, August 23, 2017 3:29 PM, Ananyev, Konstantin:
> > > > From: Shahaf Shuler
> > > > > In order to enable PMDs to support only one of the APIs, and
> > > > > applications to avoid branching according to the underlying device
> > > > > a copy functions to/from the old/new APIs were added.
> > 
> > Looks a good intent.
> > I would prefer the word "convert" instead of "copy".
> > 
> > > > >  int
> > > > >  rte_eth_rx_queue_setup(uint8_t port_id, uint16_t rx_queue_id,
> > [...]
> > > > > +	} else if ((!(dev->data->dev_flags & RTE_ETH_DEV_RXQ_OFFLOAD)) &&
> > > > > +		   (dev->data->dev_conf.rxmode.ignore == 1)) {
> > > > > +		int ret;
> > > > > +		struct rte_eth_rxmode rxmode;
> > > > > +
> > > > > +		rte_eth_copy_rxq_offloads(&rxmode, rx_conf);
> > > > > +		if (memcmp(&rxmode, &dev->data->dev_conf.rxmode,
> > > > > +			   sizeof(rxmode))) {
> > > > > +			/*
> > > > > +			 * device which work with rxmode offloads API requires
> > > > > +			 * a re-configuration in order to apply the new offloads
> > > > > +			 * configuration.
> > > > > +			 */
> > > > > +			dev->data->dev_conf.rxmode = rxmode;
> > > > > +			ret = rte_eth_dev_configure(port_id,
> > > > > +					dev->data->nb_rx_queues,
> > > > > +					dev->data->nb_tx_queues,
> > > > > +					&dev->data->dev_conf);
> > > >
> > > > Hmm, and why we would need to reconfigure our device in the middle
> > > > of rx queue setup?
> > >
> > > The reason is the old Rx offloads API is configured on device configure.
> > > This if section is for applications which already moved to the new
> > > offload API however the underlying PMD still uses the old one.
> > 
> > Isn't it risky to re-run configure here?
> > We could also declare this case as an error.
> > 
> > I think applications which have migrated to the new API, could use the
> > convert functions themselves before calling configure to support not
> > migrated PMDs.
> > The cons of my solution are:
> > - discourage apps to migrate before all PMDs have migrated
> > - expose a temporary function to convert API I propose it anyway because
> > there is always someone to like bad ideas ;)
> 
> Yes. I tried to make it as simple as possible for application to move to the new API.
> Defining it as error flow, will enforce the application to check the PMD offload mode and branch accordingly. The conversion functions are a good helpers, yet the code remains complex due to the different cases with the different PMDs.
> 
> Considering the re-configuration is risky, and without other ideas I will need to fall back to the error flow case.
> Are we OK with that?

I think we can take the risk of keeping this call to
rte_eth_dev_configure() in the middle of rte_eth_rx_queue_setup().
In theory it should be acceptable.
If we merge it soon, it can be better tested with every drivers.