netdev - Re: [net-next 01/13] net/mlx5e: Print a warning when LRO feature is dropped or not allowed

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Message-ID: <cb43e9dadb8e48d27df8f08464bf40f7a81eafe9.camel@mellanox.com>
Date:   Tue, 30 Jul 2019 20:07:59 +0000
From:   Saeed Mahameed <saeedm@...lanox.com>
To:     "willemdebruijn.kernel@...il.com" <willemdebruijn.kernel@...il.com>
CC:     Huy Nguyen <huyn@...lanox.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [net-next 01/13] net/mlx5e: Print a warning when LRO feature is
 dropped or not allowed

On Tue, 2019-07-30 at 11:52 -0400, Willem de Bruijn wrote:
> On Mon, Jul 29, 2019 at 7:50 PM Saeed Mahameed <saeedm@...lanox.com>
> wrote:
> > From: Huy Nguyen <huyn@...lanox.com>
> > 
> > When user enables LRO via ethtool and if the RQ mode is legacy,
> > mlx5e_fix_features drops the request without any explanation.
> > Add netdev_warn to cover this case.
> > 
> > Fixes: 6c3a823e1e9c ("net/mlx5e: RX, Remove HW LRO support in
> > legacy RQ")
> > Signed-off-by: Huy Nguyen <huyn@...lanox.com>
> > Signed-off-by: Saeed Mahameed <saeedm@...lanox.com>
> > ---
> >  drivers/net/ethernet/mellanox/mlx5/core/en_main.c | 5 +++--
> >  1 file changed, 3 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
> > b/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
> > index 47eea6b3a1c3..776eb46d263d 100644
> > --- a/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
> > +++ b/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
> > @@ -3788,9 +3788,10 @@ static netdev_features_t
> > mlx5e_fix_features(struct net_device *netdev,
> >                         netdev_warn(netdev, "Dropping C-tag vlan
> > stripping offload due to S-tag vlan\n");
> >         }
> >         if (!MLX5E_GET_PFLAG(params, MLX5E_PFLAG_RX_STRIDING_RQ)) {
> > -               features &= ~NETIF_F_LRO;
> > -               if (params->lro_en)
> > +               if (features & NETIF_F_LRO) {
> >                         netdev_warn(netdev, "Disabling LRO, not
> > supported in legacy RQ\n");
> 
> This warns about "Disabling LRO" on an enable request?
> 

no, this warning appears only when lro is already enabled and might
conflict with any other feature requested by user (hence
mlx5e_fix_features), e.g when moving away from striding rq in this
example, we will force lro to off.


> More fundamentally, it appears that the device does not advertise
> the feature as configurable in netdev_hw_features as of commit
> 6c3a823e1e9c ("net/mlx5e: RX, Remove HW LRO support in
> legacy RQ"), so shouldn't this be caught by the device driver
> independent ethtool code?

when hw doesn't support MLX5E_PFLAG_RX_STRIDING_RQ then yes, you will
never hit this code path, but when hw does support
MLX5E_PFLAG_RX_STRIDING_RQ and you want to turn striding rq off, then
lro will be forced to off (if it was enabled in first space) and a
warning msg will be shown.