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

["Gaëtan Rivet" <gaetan.rivet@6wind.com>]

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On Mon, Mar 25, 2019 at 02:26:27PM +0100, Gaëtan Rivet wrote:
> On Mon, Mar 25, 2019 at 11:49:20AM +0000, Ferruh Yigit wrote:
> > On 3/20/2019 11:46 AM, Thomas Monjalon wrote:
> > > 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 :)
> > > 
> > 
> > I see it can work if an application always wants this config option to have
> > *same* value. So it can set this in eal_init() always.
> > 
> > This requires "driver=xxx,key=value" kind of support in devargs.
> > 
> > 
> > John, Hyong,
> > 
> > I guess some level of devargs support is already there, Thomas/Gaetan can
> > provide more information on latest status of it, can it be possible to get some
> > support from you to finalize this effort?
> > 
> > And when it is ready enic can benefit from it for this usecase.
> > 
> > Thanks,
> > ferruh
> 
> Hi Thomas, Ferruh, John, Hyong,
> 
> driver=xxx,key=value could work, as it is not dependent on the
> devargs framework, only on the driver implementation. Nothing specific
> should be needed from EAL PoV (regarding this feature only). What will
> be missing is the new devargs support in general.

Sorry I spoke too quickly, specific development and some passing of
arguments would be needed.

> 
> Regarding the new devargs: this dev was stalled 2 versions ago at the
> --dev inclusion step. This parameter was necessary for PMD maintainers
> to be able to use the new init path with their drivers and transition to
> rte_eth_devargs_parse() for devargs parsing.
> 
> --dev was proposed, but its patch was not kept by Thomas during the
> final crunch. I probably did not shout loud enough about it and let it
> go, but I think this was a mistake: this feature was low-risk and central
> in the transition process (it was in parallel to -w/b and --vdev).
> 
> -- 
> Gaëtan Rivet
> 6WIND

-- 
Gaëtan Rivet
6WIND