netdev - RE: [PATCH net-next 00/19] Mellanox, mlx5 sub function support

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Date:   Thu, 7 Nov 2019 20:52:29 +0000
From:   Parav Pandit <parav@...lanox.com>
To:     Jakub Kicinski <jakub.kicinski@...ronome.com>
CC:     "alex.williamson@...hat.com" <alex.williamson@...hat.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Saeed Mahameed <saeedm@...lanox.com>,
        "kwankhede@...dia.com" <kwankhede@...dia.com>,
        "leon@...nel.org" <leon@...nel.org>,
        "cohuck@...hat.com" <cohuck@...hat.com>,
        Jiri Pirko <jiri@...lanox.com>,
        "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
        Or Gerlitz <gerlitz.or@...il.com>
Subject: RE: [PATCH net-next 00/19] Mellanox, mlx5 sub function support

Hi Jakub,

> -----Original Message-----
> From: Jakub Kicinski <jakub.kicinski@...ronome.com>
> Sent: Thursday, November 7, 2019 2:33 PM
> To: Parav Pandit <parav@...lanox.com>
> Cc: alex.williamson@...hat.com; davem@...emloft.net;
> kvm@...r.kernel.org; netdev@...r.kernel.org; Saeed Mahameed
> <saeedm@...lanox.com>; kwankhede@...dia.com; leon@...nel.org;
> cohuck@...hat.com; Jiri Pirko <jiri@...lanox.com>; linux-
> rdma@...r.kernel.org; Or Gerlitz <gerlitz.or@...il.com>
> Subject: Re: [PATCH net-next 00/19] Mellanox, mlx5 sub function support
> 
> On Thu,  7 Nov 2019 10:04:48 -0600, Parav Pandit wrote:
> > Mellanox sub function capability allows users to create several
> > hundreds of networking and/or rdma devices without depending on PCI SR-
> IOV support.
> 
> You call the new port type "sub function" but the devlink port flavour is mdev.
> 
Sub function is the internal driver structure. The abstract entity at user and stack level is mdev.
Hence the port flavour is mdev.
 
> As I'm sure you remember you nacked my patches exposing NFP's PCI sub
> functions which are just regions of the BAR without any mdev capability. Am I
> in the clear to repost those now? Jiri?
> 
For sure I didn't nack it. :-)
What I remember discussing offline/mailing list is 
(a) exposing mdev/sub fuctions as devlink sub ports is not so good abstraction
(b) user creating/deleting eswitch sub ports would be hard to fit in the whole usage model

> > Overview:
> > ---------
> > Mellanox ConnectX sub functions are exposed to user as a mediated
> > device (mdev) [2] as discussed in RFC [3] and further during
> > netdevconf0x13 at [4].
> >
> > mlx5 mediated device (mdev) enables users to create multiple
> > netdevices and/or RDMA devices from single PCI function.
> >
> > Each mdev maps to a mlx5 sub function.
> > mlx5 sub function is similar to PCI VF. However it doesn't have its
> > own PCI function and MSI-X vectors.
> >
> > mlx5 mdevs share common PCI resources such as PCI BAR region, MSI-X
> > interrupts.
> >
> > Each mdev has its own window in the PCI BAR region, which is
> > accessible only to that mdev and applications using it.
> >
> > Each mlx5 sub function has its own resource namespace for RDMA resources.
> >
> > mdevs are supported when eswitch mode of the devlink instance is in
> > switchdev mode described in devlink documentation [5].
> 
> So presumably the mdevs don't spawn their own devlink instance today, but
> once mapped via VIRTIO to a VM they will create one?
> 
mdev doesn't spawn the devlink instance today when mdev is created by user, like PCI.
When PCI bus driver enumerates and creates PCI device, there isn't a devlink instance for it.

But, mdev's devlink instance is created when mlx5_core driver binds to the mdev device.
(again similar to PCI, when mlx5_core driver binds to PCI, its devlink instance is created ).

I should have put the example in patch-15 which creates/deletes devlink instance of mdev.
I will revise the commit log of patch-15 to include that.
Good point.

> It could be useful to specify.
> 
Yes, its certainly useful. I missed to put the example in commit log of patch-15.

> > Network side:
> > - By default the netdevice and the rdma device of mlx5 mdev cannot
> > send or receive any packets over the network or to any other mlx5 mdev.
> 
> Does this mean the frames don't fall back to the repr by default?
Probably I wasn't clear.
What I wanted to say is, that frames transmitted by mdev's netdevice and rdma devices don't go to network.
These frames goes to representor device.
User must configure representor to send/receive/steer traffic to mdev.