Re: [EXT] Re: [RFC, net-next] net: qos: introduce a frer action to implement 802.1CB

[Vladimir Oltean]

On Fri, Oct 01, 2021 at 08:55:24PM +0300, Vladimir Oltean wrote:
> On Fri, Oct 01, 2021 at 10:27:12AM -0700, Vinicius Costa Gomes wrote:
> > Xiaoliang Yang <xiaoliang.yang_1@xxxxxxx> writes:
> > 
> > > Hi Vinicius,
> > >
> > > On Sep 29, 2021 at 6:35:59 +0000, Vinicius Costa Gomes wrote:
> > >> > This patch introduce a frer action to implement frame replication and
> > >> > elimination for reliability, which is defined in IEEE P802.1CB.
> > >> >
> > >> 
> > >> An action seems, to me, a bit too limiting/fine grained for a frame replication
> > >> and elimination feature.
> > >> 
> > >> At least I want to hear the reasons that the current hsr/prp support cannot be
> > >> extended to support one more tag format/protocol.
> > >> 
> > >> And the current name for the spec is IEEE 802.1CB-2017.
> > >> 
> > > 802.1CB can be set on bridge ports, and need to use bridge forward
> > > Function as a relay system. It only works on identified streams,
> > > unrecognized flows still need to pass through the bridged network
> > > normally.
> > 
> > This ("only on identified streams") is the strongest argument so far to
> > have FRER also as an action, in adition to the current hsr netdevice
> > approach.
> > 
> > >
> > > But current hsr/prp seems only support two ports, and cannot use the
> > > ports in bridge. It's hard to implement FRER functions on current HSR
> > > driver.
> > 
> > That the hsr netdevice only support two ports, I think is more a bug
> > than a design issue. Which will need to get fixed at some point. 
> 
> What do you mean 'a bug'? HSR and PRP, as protocols, use _two_ ports,
> see IEC 62439-3, that's where the "D" (doubly attached node) in DANH and
> DANP comes from. There's no TANH/TANH for "triply attached node".
> It doesn't scale.
> 
> > Speaking of functions, one thing that might be interesting is trying to
> > see if it makes sense to make part of the current hsr functionality a
> > "library" so it can be used by tc-frer as well. (less duplication of
> > bugs).
> 
> You mean tc-frer should inherit from the get-go the plethora of bugs
> from the unmaintained hsr driver? :)
> 
> That would be good for hsr, which is in a pretty poor state, but the
> design of the 802.1CB spec isn't really in its favor sadly.
> 
> > >
> > > You can see chapter "D.2 Example 2: Various stack positions" in IEEE 802.1CB-2017,
> > > Protocol stack for relay system is like follows:
> > >
> > >              Stream Transfer Function
> > >                 |             |
> > >   				|    	Sequence generation
> > >                 |       	Sequence encode/decode
> > >   Stream identification		Active Stream identification
> > > 				|			  |
> > >   			    |		Internal LAN---- Relay system forwarding
> > > 				|						|		|
> > > 				MAC						MAC		MAC
> > >
> > > Use port actions to easily implement FRER tag add/delete, split, and
> > > recover functions.
> > >
> > > Current HSR/PRP driver can be used for port HSR/PRP set, and tc-frer
> > > Action to be used for stream RTAG/HSR/PRP set and recover.
> > 
> > I am still reading the spec and trying to imagine how things would fit
> > together:
> >   - for which use cases tc-frer would be useful;
> >   - for which use cases the hsr netdevice would be useful;
> >   - would it make sense to have them in the same system?
> 
> You could use FRER in networks where normally you'd use HSR (aka rings).
> In fact the 802.1CB demonstration I have, which uses the NXP tsntool
> program with the downstream genetlink tsn interface, does exactly that:
> https://github.com/vladimiroltean/tsn-scripts
> 
> Basically FRER is IEEE's take on redundancy protocols and more like a
> generalization of HSR/PRP, the big changes are:
> - not limited to two (or any number of) ports
> - more than one type of stream/flow identification function: can look at
>   source/destination MAC, source/destination IP, VLAN, and most
>   importantly, there can be passive stream identification functions (don't
>   modify the packet) and active stream identification functions (do
>   modify the packet).
> 
> Please note that we've already started modeling IEEE 802.1CB stream
> identification functions as tc flower filters, since those map nicely on top.
> We use these for PSFP (former 802.1Qci) tc-police and tc-gate actions
> (yes, tc-police is single-bucket and color-unaware, that needs to be improved).
> 
> Basically IEEE 802.1CB is a huge toolbox, the spec gives you the tools
> but it doesn't tell you how to use them, that's why the stream
> identification functions are so generic and decoupled from the
> redundancy protocol itself.
> 
> In both HSR and PRP, sequence numbers are kept per source MAC address,
> that is absolutely baken into the standard.
> 
> But think about this. When the sequence number is kept per source
> station, frames sent from node A to multiple destinations (nodes B and C)
> will be part of the same stream. So nodes B and C will see
> discontinuities in the sequence numbers when node A talks to them.
> 
> The opposite is true as well. When sequence numbers are kept per
> destination MAC address, then frames sent from multiple talkers (nodes A
> and B) to the same destination (node C) will be interpreted as part of
> the same stream by the listener. So there will be jumps in sequence
> numbers seen by C when A and B are simultaneously transmitting to it.
> 
> Which type of stream identification you need depends on the traffic you
> need to support, and the topology.
> 
> So again, IEEE 802.1CB doesn't tell you what to do, but it gives you the
> tools. You can do source MAC based stream identification, and you can
> emulate HSR, or you can do something that encompasses both source node
> information as well as destination node information.
> 
> It's one whole degree of freedom more flexible, plain and simple.
> And the topologies are not limited to:
> - the rings that HSR supports
> - the disjoint IP networks that PRP supports
> but are rather generic graphs.
> 
> I fully expect there to be hardware out there already that can convert
> between the HSR/PRP frame format on one set of ports to 802.1CB frame
> format on another set of ports. Maybe that's something that some thought
> needs to be put into.

And Xiaoliang, can you PLEASE remove the following email addresses from
further submissions you make:
andre.guedes@xxxxxxxxxxxxxxx
vishal@xxxxxxxxxxx
ivan.khoronzhuk@xxxxxxxxxx
m-karicheri2@xxxxxx
Arvid.Brodin@xxxxxxxx

You also copied some of them on all 6 submissions for the PSFP offload series.
It gets really annoying to get email bounces from these addresses.
I've removed them from this email thread. Thanks.