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

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

Hi Thomas,


> -----Original Message-----
> From: Thomas Monjalon [mailto:thomas.monjalon@6wind.com]
> Sent: Thursday, June 23, 2016 1:02 AM
> To: Lu, Wenzhuo
> Cc: dev@dpdk.org
> Subject: Re: [dpdk-dev] [PATCH v3] ethdev: fix DCB config issue on ixgbe
> 
> 2016-05-06 05:33, Wenzhuo Lu:
> > An issue is found that DCB cannot be configured on ixgbe NICs. It's
> > said the TX queue number is not right.
> > On ixgbe the max TX queue number is not fixed, it depends on the
> > multi-queue mode. The API rte_eth_dev_configure should be used to
> > configure this mode. But the input of this API includes TX queue
> > number. The problem is before the mode is configured, we cannot decide
> > the TX queue number.
> >
> > This patch adds an API to configure RX & TX multi-queue mode
> > separately. After the mode is configured, the max RX & TX queue number
> > is decided. Then we can set the appropriate RX & TX queue number.
> [...]
> > +/**
> > + * Set RX & TX multi_queue mode.
> > + *
> > + * @param port_id
> > + *   The port identifier of the Ethernet device.
> > + * @param rx_mq_mode
> > + *   RX multi_queue mode.
> > + * @param tx_mq_mode
> > + *   TX multi_queue mode.
> > + *
> > + * @return
> > + *   - (0) if successful.
> > + *   - (-ENODEV) if port identifier is invalid.
> > + */
> > +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 :)