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

[Slava Ovsiienko <viacheslavo@nvidia.com>]

Hi, Jan

> -----Original Message-----
> From: Jan Viktorin <viktorin@cesnet.cz>
> Sent: Monday, March 15, 2021 21:49
> To: Slava Ovsiienko <viacheslavo@nvidia.com>
> Cc: dev@dpdk.org; Asaf Penso <asafp@nvidia.com>; Shahaf Shuler
> <shahafs@nvidia.com>; Matan Azrad <matan@nvidia.com>
> Subject: Re: [PATCH 2/2] net/mlx5: avoid unbind step to enable switchdev
> mode
> 
> On Mon, 15 Mar 2021 19:31:25 +0000
> Slava Ovsiienko <viacheslavo@nvidia.com> wrote:
> 
> > Hi, Jan
> 
> Hello Salva,
> 
> I am sorry, but I didn't get the point of your response. For me, there was 1 PF
> 0000:05:00.1, SRIOV disabled. So, I followed the guide [1].
> 
> 1. Enable SRIOV via mlxconfig. Done.
> 
> 2. Configure max number of VFs. Done.
> 
> 3. Reset firmware. Done.
> 
> In fact, I had to reboot the machine here so I am not convinced the reset of
> firmware is the thing. But I can image that there is some other use case for it.
> After reboot, I configured 2 VFs: 0000:05:00.4, 0000:05:00.5.
> 
> 4. Unbind the PF 0000:05:00.1. Done.
No, it is the second physical port. You should unbind your VFs instead - 0000:05:00.4, 0000:05:00.5.

Please, see:
> > 3. Then, we should unbind VFs ONLY, PF should be kept untouched.

With best regards,
Slava

> 
> 5. Fail, no way how to configure switchdev because of previous step.
> Thus, I strongly believe that the guide is misleading here.
> 
> When I bound the PF 0000:05:00.1 back, I could configure the switchdev
> mode and everything was just OK and seemed to be working. So **after**
> the bind I configured the switchdev mode properly.
> 
> [1] https://doc.dpdk.org/guides/nics/mlx5.html#enable-switchdev-mode
> 
> 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@cesnet.cz>
> > > Sent: Monday, March 15, 2021 18:11
> > > To: Slava Ovsiienko <viacheslavo@nvidia.com>
> > > Cc: dev@dpdk.org; Asaf Penso <asafp@nvidia.com>; Shahaf Shuler
> > > <shahafs@nvidia.com>; Matan Azrad <matan@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@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@fit.vutbr.cz>
> > > > > Sent: Monday, March 15, 2021 17:34
> > > > > To: dev@dpdk.org
> > > > > Cc: Jan Viktorin <viktorin@cesnet.cz>; Asaf Penso
> > > > > <asafp@nvidia.com>; Shahaf Shuler <shahafs@nvidia.com>; Slava
> > > > > Ovsiienko <viacheslavo@nvidia.com>; Matan Azrad
> > > <matan@nvidia.com>
> > > > > Subject: [PATCH 2/2] net/mlx5: avoid unbind step to enable
> > > > > switchdev mode
> > > > >
> > > > > From: Jan Viktorin <viktorin@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@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
> > > >
> >