On Thu, Jan 12, 2017 at 09:35:08PM +0200, Leon Romanovsky wrote: > > > In datagram mode, the IB UD (Unreliable Datagram) transport is used > > > so the MTU of the interface is equal to the IB L2 MTU minus the > > > IPoIB encapsulation header. Any request to change the MTU value > > > above the maximum range will change the MTU to the max allowed, but > > > will not show any warning message. An ipoib_warn is issued in such > > > cases, letting the user know that even though the value is legal, > > > it can't be currently applied. How does RC mode work then? > Second, I have a different view from you on the issue. User configured > some value, which is not correct for IPoIB. In ideal world (without legacy), > we were supposed to return error to him with proper message, but in our > case (legacy applications) we can't (we tried and it broke some legacy > ifcongfig, if I remember well). So it leaves us with one available > option is to warn user about improper value. This is a legitimate configuration though, the user could have a mixed MTU fabric and rely on path MTU discovery, so sets the MTU to the largest. AFAIK the way to handle such configurations is with a multicast route that has a reduced mtu. Jason -- To unsubscribe from this list: send the line "unsubscribe linux-rdma" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
