Re: [dpdk-dev] [PATCH v3] ethdev: fix DCB config issue on ixgbe

[Thomas Monjalon <thomas.monjalon@6wind.com>]

2016-06-23 01:04, Lu, Wenzhuo:
> From: Thomas Monjalon [mailto:thomas.monjalon@6wind.com]
> > 2016-05-06 05:33, Wenzhuo Lu:
> > > +int
> > > +rte_eth_dev_mq_mode_set(uint8_t port_id,
> > > +			enum rte_eth_rx_mq_mode rx_mq_mode,
> > > +			enum rte_eth_tx_mq_mode tx_mq_mode);
> > 
> > I've really tried to think about it and I think it is more or less a hack.
> > First, it is not explained in the doc when we should use
> > rte_eth_dev_mq_mode_set() instead of a simple call to rte_eth_dev_configure().
> > Second, I don't understand why having a function which configures the
> > "multiqueue modes" without configuring properly RSS/VMDq/DCB.
> > Last, it is said that rte_eth_dev_configure() "must be invoked first before any
> > other function in the Ethernet API".
> Sorry, didn't notice this announcement.
> 
> > My opinion is that the primary goal of rte_eth_dev_configure() was "Embedding
> > all configuration information in a single data structure"
> > but it is currently configuring only speed and some flow steering (only RSS,
> > VMDq, DCB and flow director).
> > This bug and the state of the ethdev API clearly shows that we must have one
> > function per feature (or group of features) and drop rte_eth_dev_configure().
> > 
> > You can argue it is a just a personal feeling and this comment comes late, but I
> > promise it is not easy to give a negative opinion because of design perspective.
> > I strongly feel we must stop workarounding the ethdev API issues and start really
> > fixing it.
> > 
> > Hope you understand and agree to work on a new API.
> I have the same feeling with you. There's some problem with rte_eth_dev_configure. So this patch is a workaround more than a real fix.
> But the problem is this API has already been used. What I think is could we take this workaround as a first step. It need not ask the APP to change too much.
> Then we can discuss how could we rework on a new API or APIs. We all know the change in rte layer is not easy and need to be very careful :)

We probably need more opinions.
I think it is not a good idea to introduce a new API only to workaround
another one and keep confusion in place.
A similar approach which looks better is to introduce a new API which will
partly replace the old one and will remain a good one when the old API
will be completely removed.
In other words, we should introduce a good API for flow steering as soon
as possible and deprecate rte_eth_dev_configure().