Re: [dpdk-dev] [PATCH v2] net/enic: add private API to set ingress VLAN rewrite mode

[Thomas Monjalon <thomas@monjalon.net>]

19/03/2019 18:29, Ferruh Yigit:
> On 3/14/2019 10:04 PM, Thomas Monjalon wrote:
> > 14/03/2019 03:58, Hyong Youb Kim:
> >> On Wed, Mar 13, 2019 at 10:29:53PM +0100, Thomas Monjalon wrote:
> >>> 13/03/2019 22:11, John Daley (johndale):
> >>>> From: Thomas Monjalon <thomas@monjalon.net>
> >>>>> 13/03/2019 19:32, Ferruh Yigit:
> >>>>>> On 3/5/2019 7:11 AM, Hyong Youb Kim wrote:
> >>>>>>> The driver currently has a devarg to set the rewrite mode during
> >>>>>>> init. Some apps want to programatically set it after running
> >>>>>>> rte_eal_init() and finding that ports are VIC. Add a private
> >>>>>>> function to support such applications.
> >>>>>>
> >>>>>> It is not good idea to have PMD specific APIs (although we already have
> >>>>> some).
> >>>>>>
> >>>>>> Specific to this case, as far as I can see it is to pass a config
> >>>>>> value and do the action related to it, what would you think having a
> >>>>>> generic key/value set/get API in ethdev for this? Similar to rawdev
> >>>>> get_attr/set_attr [1]?
> >>>>>>
> >>>>>> My concern is it may turn into something like ioctl with many things
> >>>>>> pushed to it, and cause possible duplication ...
> >>>>>
> >>>>> Yes, it is clearly ioctl style.
> >>>>>
> >>>>> Please could you explain more what is the rewrite mode?
> >>>>> Does it apply to the port or the queue?
> >>>>>
> >>>> It applies to a port. By default the Cisco VIC VLAN tags every packet on ingress even if they were untagged coming in on the wire. They are tagged with VLAN 0 or a VLAN id programmed into the NIC depending on the configuration. Its part of the original design, to maintain priority bits, ancient history.
> >>>>
> >>>> Some apps don't like this (VPP) or take a slower path (OVS). Hyong added a ig-vlan-rewrite=untag devarg to disable this (leave untagged/default vlan packets untagged) during rte_eal_init and this is helpful for OVS, but VPP likes to set the rewrite mode after rte_eal_init() and finding the ports are VIC ports. So that is the reasoning behind the private API call.
> >>>
> >>> It looks like an application will always set this flag or never.
> >>> So I don't see the need for an API function.
> >>> Why VPP prefers set this flag later?
> >>> Would it be better to have some driver-specific flags, no matter the ports?
> >>
> >> As is, there seem to be two ways apps deal with NIC-specific tweaks/quirks.
> >>
> >> 1. Leave everything to the user.
> >>
> >> Let the human user specify NIC-specific settings (e.g. devarg,
> >> not-so-standard MTU/MRU, offloads with not-so-uniform behavior). The
> >> app simply passes these to DPDK and does nothing else. Devargs are
> >> passed to rte_eal_init. Other settings are applied during the
> >> configure phase after rte_eal_init.
> >>
> >> For example, OVS seems to go for a smallest common denominator that
> >> works with most NICs out of the box. Otherwiese, it kinda falls into
> >> this camp.
> >>
> >> For a problematic NIC that needs user intervention, troubleshooting
> >> goes like this :-)
> >> - Install app.
> >> - Run with settings that worked on a previous machine.
> >> - Some features suddenly do not work.
> >> - Google search this and that ("why this does not work on this server?").
> >> - Contact vendors.
> >> - Find out this NIC has unexpected behavior.
> >> - Set devarg, tweak MTU/MRU, ... ("Oh need to set this for ..").
> >> - Now the features work.
> >>
> >> 2. Hide ugly tweaks from the user.
> >>
> >> VPP falls into this camp. The user specifies BDFs in the config (no
> >> devargs). The app calls rte_eal_init(BDFs), iterates through the
> >> discovered ports, applies whatever NIC-specific settings necessary
> >> during the configure phase (i.e. do this for vendor A NIC, do that for
> >> vendor B NIC), and then start the ports.
> >>
> >> The ingress vlan rewrite mode is devarg now, so is not usable in this
> >> model. One way around it is a private API. Driver specific flags
> >> during the configure phase would also work fine. Though, enic might be
> >> the only user of those flags.
> > 
> > I think DPDK needs some driver configuration.
> > Currently the config is done per device with devargs.
> > The next devargs format allow this:
> > 	driver=enic,rewrite=on
> > and it can be passed to rte_eal_init().
> > 
> > We did not progress on the implementation of this format in recent months,
> > but you are welcome to help!
> > Instead of passing devargs in the whitelist/blacklist options,
> > we should introduce a new option, like --dev.
> 
> But it will be still devarg in new implementation.

With the new syntax, no need to specify a device.
We can match a driver or multiple drivers sharing the same property.

> I guess for this use case, there is a need to pass this information from an API.
> Options can be:
> 1- PMD specific API
> 2- Extend ethdev dev_ops for each usecase
> 3- Have a generic API, as suggested above
> 4- Extend configure to accept flags
> 
> I don't see a winner in above list, each has some problems. Any comment on how
> to proceed?

I don't see a problem with the devargs approach.