On Mon, Jan 16, 2017 at 01:12:18PM -0700, Jason Gunthorpe wrote:
> On Sun, Jan 15, 2017 at 10:35:43AM +0200, Leon Romanovsky wrote:
> > On Fri, Jan 13, 2017 at 02:27:21PM -0700, Jason Gunthorpe wrote:
> > > On Fri, Jan 13, 2017 at 10:31:27PM +0200, Leon Romanovsky wrote:
> > >
> > > > > This is about what happens if the multicast MTU < unicast MTU - which
> > > > > is *exactly* the same case on RC and UD.
> > > > >
> > > > > IPoIB cannot send a 64k multicast MTU on RC either.
> > > >
> > > > Multicast is sent in datagram despite being in connected mode and for
> > > > datagram the MTU is limited by IB
> > >
> > > I am aware of that. Read you patch again:
> > >
> > > > +	if (priv->mcast_mtu < priv->admin_mtu)
> > > > +		ipoib_warn(priv, "MTU must be smaller than mcast_mtu (%u)\n",
> > >
> > > This check is fails in RC mode as well.
> > >
> > > And we already check if the requested MTU is beyond the port
> > > capability:
> > >
> > > +        if (new_mtu > IPOIB_UD_MTU(priv->max_ib_mtu))
> > > +                return -EINVAL;
> > >
> > > So I have *no idea* why you'd want to check it against the multicast
> > > group too..
> > >
> >
> > Port MTU capability can be higher than link MTU. In this flow, the user
> > can try to set manually MTU which will be higher than SM provided.
> >
> > Immediately after that print, we have a following piece of code:
> >  236         dev->mtu = min(priv->mcast_mtu, priv->admin_mtu);
>
> Maybe the better fix is to take that min out than generate a
> warning.

It looks like that I need more time to grasp it.
Sorry about that.

>
> Jason