Re: [PATCH] net/mlx5: avoid setting kernel MTU if not needed

[Dariusz Sosnowski <dsosnowski@nvidia.com>]

On Tue, Jun 03, 2025 at 07:53:45PM +0200, Dariusz Sosnowski wrote:
> Hi,
> 
> On Wed, May 28, 2025 at 02:12:37PM +0200, David Marchand wrote:
> > Hello,
> > 
> > On Wed, May 28, 2025 at 11:36 AM Maxime Coquelin
> > <maxime.coquelin@redhat.com> wrote:
> > >
> > > This patch checks whether the Kernel MTU has the same value
> > > as the requested one at port configuration time, and skip
> > > setting it if it is the same.
> > >
> > > Doing this, we can avoid the application to require
> > > NET_ADMIN capability, as in v23.11.
> > >
> > > Fixes: 10859ecf09c4 ("net/mlx5: fix MTU configuration")
> > > Cc: stable@dpdk.org
> > >
> > > Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
> > > ---
> > >
> > > Hi Dariuz,
> > >
> > > I set priv->mtu as it is done after the mlx5_set_mtu() call,
> > > but I'm not sure it is necessary, as is the existing call to
> > > mlx5_get_mtu() because it seems done in mlx5_dev_spawn().
> 
> Correct, this additional update of priv->mtu is not needed here.
> It can be removed.
> 
> > 
> > It seems there were some back and forth on this priv->mtu topic
> > between Nelio and other devs in the past.
> > 
> > Atm, I don't see the need for keeping such a cached mtu value in priv.
> > There is only one user of the value, and it is for configuration
> > operation that can do a query to the kernel.
> 
> I agree. It's not really needed, especially since the same value is also
> stored in dev->data->mtu, so the kernel query can easily be replaced
> with reading dev->data->mtu.

Correction - "so the use of cached value can easily be replaced with
reading dev->data->mtu".