[dpdk-dev] [PATCH 2/2] net/mlx5: avoid unbind step to enable switchdev mode

[Slava Ovsiienko]

Hi, Jan

1. Let's suppose we have the one port NIC, PCI BDF 08:00.0, SR-IOV enabled, 0 VFs is configured,
netdev name is ens1f0 (depends on distro and kernel version). 

2. Then, we configure 3 VFs with SR-IOV, we get :
- 08:00.0 - PF, ens1f0
- 08:00.1 - VF0, ens1f1
- 08:00.2 - VF1, ens1f2
- 08:00.3 - VF2, ens1f3

3. Then, we should unbind VFs ONLY, PF should be kept untouched.
- 08:00.0 - PF, ens1f0
- 08:00.1 - VF0, -
- 08:00.2 - VF1, -
- 08:00.3 - VF2, -

4. Then, configure switchdev mode
- 08:00.0 - PF, ens1f0
- 08:00.1 - VF0, -
- 08:00.2 - VF1, -
- 08:00.3 - VF2, -
+ we get 3 representor netdevs:
ens1f0_0 (no dedicated PCI device)
ens1f0_1 (no dedicated PCI device)
ens1f0_2 (no dedicated PCI device)

5. Then, bind VFs back (assume we are no going to map them to VMs)
- 08:00.0 - PF, ens1f0
- 08:00.1 - VF0, ens1f1
- 08:00.2 - VF1, ens1f2
- 08:00.3 - VF2, ens1f3
- ens1f0_0 (no dedicated PCI device)
- ens1f0_1 (no dedicated PCI device)
- ens1f0_2 (no dedicated PCI device)

6. As result we should get 7 netdevs - 1 PF (Uplink representor), 3 VFs, 3 representors (no PCI device, pure netdev)

With best regards, Slava

> -----Original Message-----
> From: Jan Viktorin <viktorin at cesnet.cz>
> Sent: Monday, March 15, 2021 18:11
> To: Slava Ovsiienko <viacheslavo at nvidia.com>
> Cc: dev at dpdk.org; Asaf Penso <asafp at nvidia.com>; Shahaf Shuler
> <shahafs at nvidia.com>; Matan Azrad <matan at nvidia.com>
> Subject: Re: [PATCH 2/2] net/mlx5: avoid unbind step to enable switchdev
> mode
> 
> Hello Salva,
> 
> On Mon, 15 Mar 2021 15:53:51 +0000
> Slava Ovsiienko <viacheslavo at nvidia.com> wrote:
> 
> > Hi, Jan
> >
> > Yes, bullet [4] explicitly requires to unbind VFs, and detach the netdevs
> from the mlx5_core driver.
> > Otherwise, kernel driver refuses to be configured with switchdev mode in
> [5]. So, [4] can't be skipped.
> > After setting swithdev mode, VFs can be bound back (if it is needed, and
> these ones are not mapped to VMs):
> 
> OK, but I believe that it is **not possible** to follow the rule [5].
> The guide explicitly says in [4] "can be rebind **after** the switchdev
> mode".
> Just, if you unbind the device, there is no way how to configure the
> switchdev mode, this is the contradiction I mentioned in the commit. You
> cannot configure switchdev mode because the interface is gone and the path
> /sys/class/net/<net device>/compat/devlink/mode no longer exists.
> 
> So, maybe, just the formulation is wrong. So, what is the **exact
> right** way how to do it? I would change the commit accordingly. Just, let's
> make it right. Would it work this way?
> 
>  # echo -n "<device pci address>" > /sys/bus/pci/drivers/mlx5_core/unbind
>  # echo -n "<device pci address>" > /sys/bus/pci/drivers/mlx5_core/bind
>  # echo switchdev > /sys/class/net/<net device>/compat/devlink/mode
> 
> It is good to mention that after the rebind, the <net device> can change.
> 
> Regards,
> Jan
> 
> >
> > echo -n "<device pci address>" > > /sys/bus/pci/drivers/mlx5_core/bind
> >
> > With best regards,
> > Slava
> >
> > > -----Original Message-----
> > > From: Jan Viktorin <iviktorin at fit.vutbr.cz>
> > > Sent: Monday, March 15, 2021 17:34
> > > To: dev at dpdk.org
> > > Cc: Jan Viktorin <viktorin at cesnet.cz>; Asaf Penso
> > > <asafp at nvidia.com>; Shahaf Shuler <shahafs at nvidia.com>; Slava
> > > Ovsiienko <viacheslavo at nvidia.com>; Matan Azrad
> <matan at nvidia.com>
> > > Subject: [PATCH 2/2] net/mlx5: avoid unbind step to enable switchdev
> > > mode
> > >
> > > From: Jan Viktorin <viktorin at cesnet.cz>
> > >
> > > The step 4 is a contradiction. It advices to unbind the device from
> > > the mlx5_core which removes the associated system network interface
> (e.g.
> > > eth0). In the step 5, the same system network interface (e.g. eth0)
> > > is required to exist.
> > >
> > > Signed-off-by: Jan Viktorin <viktorin at cesnet.cz>
> > > ---
> > >  doc/guides/nics/mlx5.rst | 6 +-----
> > >  1 file changed, 1 insertion(+), 5 deletions(-)
> > >
> > > diff --git a/doc/guides/nics/mlx5.rst b/doc/guides/nics/mlx5.rst
> > > index 0a2dc3dee..122d8e0fc 100644
> > > --- a/doc/guides/nics/mlx5.rst
> > > +++ b/doc/guides/nics/mlx5.rst
> > > @@ -1370,11 +1370,7 @@ the DPDK application.
> > >
> > >          echo <num of vfs > /sys/class/net/<net
> > > device>/device/sriov_numvfs
> > >
> > > -4. Unbind the device (can be rebind after the switchdev mode)::
> > > -
> > > -        echo -n "<device pci address>" >
> > > /sys/bus/pci/drivers/mlx5_core/unbind
> > > -
> > > -5. Enable switchdev mode::
> > > +4. Enable switchdev mode::
> > >
> > >          echo switchdev > /sys/class/net/<net
> > > device>/compat/devlink/mode
> > >
> > > --
> > > 2.30.1
> >