From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jason Gunthorpe Subject: Re: [PATCH rdma-next V1 1/9] IB/ipoib: Add warning message when changing the MTU in UD over the max range Date: Fri, 13 Jan 2017 14:27:21 -0700 Message-ID: <20170113212721.GB1463@obsidianresearch.com> References: <20161228124728.26619-1-leon@kernel.org> <20161228124728.26619-2-leon@kernel.org> <1484246776.123135.19.camel@redhat.com> <20170112193508.GO20392@mtr-leonro.local> <20170112201622.GA14584@obsidianresearch.com> <20170113150824.GQ20392@mtr-leonro.local> <20170113171234.GA30551@obsidianresearch.com> <20170113203127.GT20392@mtr-leonro.local> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20170113203127.GT20392-U/DQcQFIOTAAJjI8aNfphQ@public.gmane.org> Sender: linux-rdma-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Leon Romanovsky Cc: Doug Ledford , linux-rdma-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Feras Daoud , Noa Osherovich List-Id: linux-rdma@vger.kernel.org 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.. It is OK for the multicast group to have a smaller MTU than the unicast side. This is how RC operates after all. Jason -- To unsubscribe from this list: send the line "unsubscribe linux-rdma" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html