netdev - Re: [PATCH net-next 2/8] devlink: add PF and VF port flavours

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Date:   Wed, 27 Feb 2019 14:42:39 -0800
From:   Jakub Kicinski <jakub.kicinski@...ronome.com>
To:     Jiri Pirko <jiri@...nulli.us>
Cc:     davem@...emloft.net, oss-drivers@...ronome.com,
        netdev@...r.kernel.org
Subject: Re: [PATCH net-next 2/8] devlink: add PF and VF port flavours

On Wed, 27 Feb 2019 21:17:27 +0100, Jiri Pirko wrote:
> Wed, Feb 27, 2019 at 06:23:26PM CET, jakub.kicinski@...ronome.com wrote:
> >On Wed, 27 Feb 2019 13:41:35 +0100, Jiri Pirko wrote:  
> >> Wed, Feb 27, 2019 at 01:23:27PM CET, jiri@...nulli.us wrote:  
> >> >Tue, Feb 26, 2019 at 07:24:30PM CET, jakub.kicinski@...ronome.com wrote:    
> >> >>Current port flavours cover simple switches and DSA.  Add PF
> >> >>and VF flavours to cover "switchdev" SR-IOV NICs.
> >> >>
> >> >>Example devlink user space output:
> >> >>
> >> >>$ devlink port
> >> >>pci/0000:82:00.0/0: type eth netdev p4p1 flavour physical
> >> >>pci/0000:82:00.0/10000: type eth netdev eth0 flavour pcie_pf pf 0
> >> >>pci/0000:82:00.0/10001: type eth netdev eth1 flavour pcie_vf pf 0 vf 0
> >> >>pci/0000:82:00.0/10002: type eth netdev eth2 flavour pcie_vf pf 0 vf 1    
> >> >
> >> >Wait a second, howcome pf and vfs have the same PCI address?    
> >> 
> >> Oh, I think you have these as eswitch port representors. Confusing...  
> >
> >FWIW I don't like the word representor, its a port. We don't call
> >physical ports "representors" even though from ASIC's point of view
> >they are exactly the same.  
> 
> My point is, they are not PFs and VFs. We have to find a way to clearly
> see what's what.

Okay, so let me explain the way I see it, and you can explain your way
or tell me where you disagree.  Those devlink ports and netdevs are pf
ports and vf ports, which most refer to as "representor".  If one sends
packets to the netdev indicated in DEVLINK_ATTR_PORT_NETDEV_*
attributes they will _egress_ the switch from that port.  For physical
port that means going onto the Ethernet or IB wire.  For PCIe it means
getting DMAed over the PCIe link to host memory.

There is a netdev construct on the host which is in charge of that 
host memory.  Maybe we shall call that host netdev?

(I said I don't like "representor" for the reason that people don't
refer to the physical port as "representor" even though it has exactly
the semantics we are following.  This distinction between behaviour of
physical and PCI ports is what leads to confusion, I think.)

Let me bring out the moose :)

                    HOST A             ||          HOST B                  
                                       ||                                  
        PF A       | V | V | V | V     ||       PF B        | V | V | V               
                   |*F |*F |*F |*F ... ||                   |*F |*F |*F ...           
*port A0 |*port A1 | 0 | 1 | 2 | 3     ||*port B0 |*port B1 | 0 | 1 | 2            
                                       ||                                  
             PCI Express link          ||        PCI Express link          
        \      \      \  |   |   |          |       |      /   /   /         
         \      \      \ |   |   |          |       |     /   /   /          
      /\  \______\______\'___|___|__________|_______'____/___/___/__    /\
      ||  |+PF0s0|+PF0s1 |+VF0|+VF1| ...|   |+PF1s0|+PF1s1|+VF0|+VF1|   ||  
  i   ||  |------ ------ ----- ---- ----|--- ------ ------ ---- ----|   ||   i
d n H ||  |               <<==========                              |   || d n H
e s O ||  |                            ==========>>                 |   || e s O
v t S ||  |                    SR-IOV e-switch                      |   || v t S
l a T ||  |               <<==========                              |   || l a T
i n   ||  |                            ==========>>                 |   || i n
n c A ||  |               ________ _________ ________               |   || n c B
k e   ||  |              |+Phys 0 |+Phys 1  |+Phys 2 |              |   || k e
      ||  \---------------------------------------------------------/   ||                 
      \/                      |        |         |                      \/    
                              |        |         |                          
                                 ||         ||                               
                          MAC 0  ||  MAC 1  || MAC 2                   
                                 ||         ||                              

Things marked with + are devlink ports and have port (-repr-) netdevs
(including physical ports).
Things marked with * are host netdevs, don't have devlink ports.