[dpdk-dev] [PATCH v3] i40e: configure MTU

[Ananyev, Konstantin]

> -----Original Message-----
> From: dev [mailto:dev-bounces at dpdk.org] On Behalf Of Xing, Beilei
> Sent: Monday, June 20, 2016 5:50 AM
> To: Yong Wang; Olivier Matz; Wu, Jingjing
> Cc: dev at dpdk.org; Julien Meunier; Thomas Monjalon
> Subject: Re: [dpdk-dev] [PATCH v3] i40e: configure MTU
> 
> 
> > -----Original Message-----
> > From: Yong Wang [mailto:yongwang at vmware.com]
> > Sent: Friday, June 17, 2016 1:40 AM
> > To: Olivier Matz <olivier.matz at 6wind.com>; Xing, Beilei <beilei.xing at intel.com>;
> > Wu, Jingjing <jingjing.wu at intel.com>
> > Cc: dev at dpdk.org; Julien Meunier <julien.meunier at 6wind.com>; Thomas
> > Monjalon <thomas.monjalon at 6wind.com>
> > Subject: Re: [dpdk-dev] [PATCH v3] i40e: configure MTU
> >
> > On 5/16/16, 5:27 AM, "dev on behalf of Olivier Matz" <dev-bounces at dpdk.org
> > on behalf of olivier.matz at 6wind.com> wrote:
> >
> > >Hi Beilei,
> > >
> > >On 05/13/2016 10:15 AM, Beilei Xing wrote:
> > >> This patch enables configuring MTU for i40e.
> > >> Since changing MTU needs to reconfigure queue, stop port first before
> > >> configuring MTU.
> > >>
> > >> Signed-off-by: Beilei Xing <beilei.xing at intel.com>
> > >> ---
> > >> v3 changes:
> > >>  Add frame size with extra I40E_VLAN_TAG_SIZE.
> > >>  Delete i40e_dev_rx_init(pf) cause it will be called when port starts.
> > >>
> > >> v2 changes:
> > >>  If mtu is not within the allowed range, return -EINVAL instead of -EBUSY.
> > >>  Delete rxq reconfigure cause rxq reconfigure will be finished in
> > >> i40e_dev_rx_init.
> > >>
> > >>  drivers/net/i40e/i40e_ethdev.c | 34
> > >> ++++++++++++++++++++++++++++++++++
> > >>  1 file changed, 34 insertions(+)
> > >>
> > >> [...]
> > >> +static int
> > >> +i40e_dev_mtu_set(struct rte_eth_dev *dev, uint16_t mtu) {
> > >> +	struct i40e_pf *pf = I40E_DEV_PRIVATE_TO_PF(dev->data->dev_private);
> > >> +	struct rte_eth_dev_data *dev_data = pf->dev_data;
> > >> +	uint32_t frame_size = mtu + ETHER_HDR_LEN
> > >> +			      + ETHER_CRC_LEN + I40E_VLAN_TAG_SIZE;
> > >> +	int ret = 0;
> > >> +
> > >> +	/* check if mtu is within the allowed range */
> > >> +	if ((mtu < ETHER_MIN_MTU) || (frame_size > I40E_FRAME_SIZE_MAX))
> > >> +		return -EINVAL;
> > >> +
> > >> +	/* mtu setting is forbidden if port is start */
> > >> +	if (dev_data->dev_started) {
> > >> +		PMD_DRV_LOG(ERR,
> > >> +			    "port %d must be stopped before configuration\n",
> > >> +			    dev_data->port_id);
> > >> +		return -ENOTSUP;
> > >> +	}
> > >
> > >I'm not convinced that ENOTSUP is the proper return value here.
> > >It is usually returned when a function is not implemented, which is not
> > >the case here: the function is implemented but is forbidden because the
> > >port is running.
> > >
> > >I saw that Julien commented on your v1 that the return value should be
> > >one of:
> > > - (0) if successful.
> > > - (-ENOTSUP) if operation is not supported.
> > > - (-ENODEV) if *port_id* invalid.
> > > - (-EINVAL) if *mtu* invalid.
> > >
> > >But I think your initial value (-EBUSY) was fine. Maybe it should be
> > >added in the API instead, with the following description:
> > >  (-EBUSY) if the operation is not allowed when the port is running
> >
> > AFAICT, the same check is not done for other drivers that implement the mac_set
> > op. Wouldn’t it make more sense to have the driver disable the port,
> > reconfigure and re-enable it in this case, instead of returning error code?  If the
> > consensus in DPDK is to have the application disable the port first, we need to
> > enforce this policy across all devices and clearly document this behavior.
> >
> Hi,
> For ixgbe/igb, there's register for MTU during runtime, but for i40e, setting MTU is finished by firmware during configuration. There'll
> be some risk when disable the port, reconfigure and re-enable the port, so return error code in this case currently.

Ok, but then what is the point to introduce mtu_set() for i40e at all?
Let's just leave it unimplemented, as it is right now.
Then users would know that for that device they have to do dev_stop/dev_configure().
Konstantin

> Thanks for your comments, we'll improve the document later.
> 
> > >This would allow the application to take its dispositions to stop the
> > >port and restart it with the proper jumbo_frame argument.
> > >
> > >+CC Thomas which maintains ethdev API.
> > >
> > >
> > >Regards,
> > >Olivier