Re: [dpdk-dev] [PATCH v2] ethdev: fix device info getting

["Lu, Wenzhuo" <wenzhuo.lu@intel.com>]

Hi Andrew,

> -----Original Message-----
> From: Andrew Rybchenko [mailto:arybchenko@solarflare.com]
> Sent: Friday, July 13, 2018 4:03 PM
> To: Lu, Wenzhuo <wenzhuo.lu@intel.com>; dev@dpdk.org
> Cc: Yigit, Ferruh <ferruh.yigit@intel.com>; Thomas Monjalon
> <thomas@monjalon.net>
> Subject: Re: [dpdk-dev] [PATCH v2] ethdev: fix device info getting
> 
> Hi, Wenzhuo,
> 
> I'm sorry, but I have more even harder questions than the previous one.
> This questions are rather generic and mainly to ethdev maintainers.
> 
> On 13.07.2018 05:42, Wenzhuo Lu wrote:
> > The device information cannot be gotten correctly before the
> > configuration is set. Because on some NICs the information has
> > dependence on the configuration.
> 
> Thinking about it I have the following question. Is it valid behaviour of the
> dev_info if it changes after configuration?
> I always thought that the primary goal of the dev_info is to provide
> information to app about device capabilities to allow app configure device
> and queues correctly. Now we see the case when dev_info changes on
> configure. May be it is acceptable, but it is really suspicious. If we accept it, it
> should be documented.
> May be dev_info should be split into parts: part which is persistent and part
> which may depend on device configuration.
As I remember, the similar discussion has happened :) I've raised the similar suggestion like this. But we don’t make it happen.
The reason is, you see, this is the rte layer's behavior. So the user doesn't have to know it. From APP's PoV, it inputs the configuration, it calls this API "rte_eth_dev_configure". It doesn't know  the configuration is copied before getting the info or not.
So, to my opinion, we can still keep the behavior. We only need to split it into parts when we do see the case that cannot make it.

> 
> > Fixes: 3be82f5cc5e3 ("ethdev: support PMD-tuned Tx/Rx parameters")
> > Signed-off-by: Wenzhuo Lu <wenzhuo.lu@intel.com>
> > ---
> >   lib/librte_ethdev/rte_ethdev.c | 21 +++++++++++----------
> >   1 file changed, 11 insertions(+), 10 deletions(-)
> >
> > diff --git a/lib/librte_ethdev/rte_ethdev.c
> > b/lib/librte_ethdev/rte_ethdev.c index 3d556a8..6f606c1 100644
> > --- a/lib/librte_ethdev/rte_ethdev.c
> > +++ b/lib/librte_ethdev/rte_ethdev.c
> > @@ -1022,6 +1022,17 @@ struct rte_eth_dev *
> >   	RTE_FUNC_PTR_OR_ERR_RET(*dev->dev_ops->dev_infos_get, -
> ENOTSUP);
> >   	RTE_FUNC_PTR_OR_ERR_RET(*dev->dev_ops->dev_configure, -
> ENOTSUP);
> >
> > +	if (dev->data->dev_started) {
> > +		RTE_ETHDEV_LOG(ERR,
> > +			"Port %u must be stopped to allow configuration\n",
> > +			port_id);
> > +		return -EBUSY;
> > +	}
> > +
> > +	/* Copy the dev_conf parameter into the dev structure,
> > +	 * then get the info.
> > +	 */
> > +	memcpy(&dev->data->dev_conf, &local_conf,
> > +sizeof(dev->data->dev_conf));
> 
> It is not a problem of the patch, but I'd like to highlight it to Ferruh and
> Thomas. What we have in the case of below failures? State is really
> inconsistent in the case of reconfigure. We have applied new dev_conf, but
> we still have previous Rx/Tx queues which were setup before.
> 
> >   	rte_eth_dev_info_get(port_id, &dev_info);
> >
> >   	/* If number of queues specified by application for both Rx and Tx
> > is @@ -1053,16 +1064,6 @@ struct rte_eth_dev *
> >   		return -EINVAL;
> >   	}
> >
> > -	if (dev->data->dev_started) {
> > -		RTE_ETHDEV_LOG(ERR,
> > -			"Port %u must be stopped to allow configuration\n",
> > -			port_id);
> > -		return -EBUSY;
> > -	}
> > -
> > -	/* Copy the dev_conf parameter into the dev structure */
> > -	memcpy(&dev->data->dev_conf, &local_conf, sizeof(dev->data-
> >dev_conf));
> > -
> >   	/*
> >   	 * Check that the numbers of RX and TX queues are not greater
> >   	 * than the maximum number of RX and TX queues supported by the