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); > It is OK for the multicast group to have a smaller MTU than the > unicast side. This is how RC operates after all. > > Jason
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