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

[Thomas Monjalon <thomas@monjalon.net>]

20/03/2019 11:45, Ferruh Yigit:
> On 3/19/2019 8:30 PM, Thomas Monjalon wrote:
> > 19/03/2019 19:00, Ferruh Yigit:
> >> On 3/19/2019 5:36 PM, Thomas Monjalon wrote:
> >>> 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.
> >>
> >> Devargs either passed via command line to DPDK application, or parameter to
> >> hotplug APIs.
> > 
> > The application can pass whatever it wants to EAL.
> 
> This means changing current device probe logic completely, right.
> Instead of probing everything on start, probe nothing and application add
> devices via eal (hotplug) API calls with providing devargs.
> I have no issue with this picture, only it doesn't look soon.

No, I mean probe everything at startup automatically as usual.
Just need to pass an option to the driver
during its initialization.

> > In the case described above, the application wants to enable
> > a mode of the driver for all its devices.
> > That's why I think the right solution is a driver option,
> > which can be achieved with the new devargs syntax.
> > 
> >> If someone wants to use regular probe without any command line argument, and
> >> later configure the device via an API, can devargs be used?
> > 
> > This is a scenario different of what is asked above.
> > In the case of a specific configuration of one device,
> > we have three choices.
> > These are your suggestions, with my comments:
> > 	1- PMD specific API
> > 	2- Extend ethdev dev_ops for each usecase
> > 	(3- Have a generic API) = choice 2
> > 	(4- Extend configure to accept flags) = choice 1
> > This is a choice 3:
> > 	- no support of exotic features
> 
> Not sure if this is a real option for a vendor, HWs has exotic features and they
> want to enable it, I believe SW should not be the blocker for this.
> 
> Also I definitely agree that exotic features should not break main/common usage,
> make it hard to use or make it confusing/complex etc.
> 
> Until we have a better solution I guess we need to continue with private APIs.

I think the driver option would work,
but it seems I fail to correctly explain it :)