netdev - Re: [PATCH net-next 00/13] Add mlx5 subfunction support

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Date:   Wed, 18 Nov 2020 22:22:51 -0800
From:   Saeed Mahameed <saeed@...nel.org>
To:     Jakub Kicinski <kuba@...nel.org>, Parav Pandit <parav@...dia.com>
Cc:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        Jiri Pirko <jiri@...dia.com>, Jason Gunthorpe <jgg@...dia.com>,
        "dledford@...hat.com" <dledford@...hat.com>,
        Leon Romanovsky <leonro@...dia.com>,
        "davem@...emloft.net" <davem@...emloft.net>
Subject: Re: [PATCH net-next 00/13] Add mlx5 subfunction support

On Wed, 2020-11-18 at 18:23 -0800, Jakub Kicinski wrote:
> On Tue, 17 Nov 2020 18:50:57 +0000 Parav Pandit wrote:
> > At this point vdpa tool of [1] can create one or more vdpa net
> > devices on this subfunction device in below sequence.
> > 
> > $ vdpa parentdev list
> > auxiliary/mlx5_core.sf.4
> >   supported_classes
> >     net
> > 
> > $ vdpa dev add parentdev auxiliary/mlx5_core.sf.4 type net name
> > foo0
> > 
> > $ vdpa dev show foo0
> > foo0: parentdev auxiliary/mlx5_core.sf.4 type network parentdev
> > vdpasim vendor_id 0 max_vqs 2 max_vq_size 256
> > 
> > > I'm asking how the vdpa API fits in with this, and you're showing
> > > me the two
> > > devlink commands we already talked about in the past.  
> > Oh ok, sorry, my bad. I understood your question now about relation
> > of vdpa commands with this.
> > Please look at the above example sequence that covers the vdpa
> > example also.
> > 
> > [1] 
> > https://lore.kernel.org/netdev/20201112064005.349268-1-parav@nvidia.com/
> 
> I think the biggest missing piece in my understanding is what's the
> technical difference between an SF and a VDPA device.
> 

Same difference as between a VF and netdev.
SF == VF, so a full HW function.
VDPA/RDMA/netdev/SCSI/nvme/etc.. are just interfaces (ULPs) sharing the
same functions as always been, nothing new about this.

Today on a VF we load a RDMA/VDPA/netdev interfaces
SF will do exactly the same and the ULPs will simply load, and we don't
need to modify them.

> Isn't a VDPA device an SF with a particular descriptor format for the
> queues?
No :/, 
I hope the above answer clarifies things a bit.
SF is a device function that provides all kinds of queues.