netdev - Re: [PATCH net-next 1/2] net: typhoon: implement ndo_features

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Date:   Fri, 4 Feb 2022 20:38:08 -0800
From:   Eric Dumazet <edumazet@...gle.com>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     Eric Dumazet <eric.dumazet@...il.com>,
        "David S . Miller" <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next 1/2] net: typhoon: implement ndo_features_check method

On Fri, Feb 4, 2022 at 8:34 PM Jakub Kicinski <kuba@...nel.org> wrote:
>
> On Fri, 4 Feb 2022 20:26:58 -0800 Eric Dumazet wrote:
> > > Should we always clear SG? If we want to make the assumption that
> > > non-gso skbs are never this long (like the driver did before) then
> > > we should never clear SG. If we do we risk one of the gso-generated
> > > segs will also be longer than 32 frags.
> >
> > If I read the comment (deleted in this patch), it seems the 32 limits
> > is about TSO only ?
> >
> > #warning Typhoon only supports 32 entries in its SG list for TSO, disabling TSO
> >
> > This is why I chose this implementation.
>
> Right, sort of my point - to stay true to old code we don't need to
> worry about SG ? The old code didn't..

I misread your comment.

I thought you suggested to always clear SG, regardless of GSO or not, as in

       if (skb_shinfo(skb)->nr_frags > 32) {
               if (skb_is_gso(skb))
                       features &= ~NETIF_F_GSO_MASK;
               features &= ~NETIF_F_SG;
       }


>
> > > Thought I should ask.
> > >
> > > > +     }
> > > > +     return features;
> > >
> > > return vlan_features_check(skb, features) ?
> >
> > Hmm... not sure why we duplicate vlan_features_check() &
> > vxlan_features_check() in all ndo_features_check() handlers :/
>
> I was wondering as well. I can only speculate.. :S