On Mon, Sep 13, 2021 at 01:38:43PM +0300, Leon Romanovsky wrote:

On Wed, Sep 08, 2021 at 01:43:28PM +0200, Christoph Lameter wrote:

quoted

ROCE uses IGMP for Multicast instead of the native Infiniband system where
joins are required in order to post messages on the Multicast group.

According to the IBTA v1.5, there is no need to join multicast group to
send messages.

 10.5.2 MULTICAST WORK REQUESTS
 10.5.2.1 IBA UNRELIABLE MULTICAST WORK REQUESTS
  ...
  A QP is not required to be attached to a Multicast Group
  in order to initiate an IBA Unreliable Multicast Work Request.

Did I look in wrong place?

This is talking about the ibv_attach_mcast() verb, which is different
from the SM notion of a node being joined to a multicast group or not.

In IBA a node that is not joined to a MGID will not be able to send to
that MGID, the network is allowed to drop the packet.

With ethernet all nodes can always send to all multicast addresses,
the IGMP stuff is only required to receive

Jason