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From: Steve Wise (swise_at_[hidden])
Date: 2007-05-08 15:52:59


On Tue, 2007-05-08 at 13:57 -0400, Andrew Friedley wrote:
> Steve Wise wrote:
> >> Well I've tried OMPI on ofed-1.2 udapl today and it doesn't work. I'm
> >> debugging now.
> >>
> >
> > Here's part of the problem (from ompi/btl/udapl/btl_udapl.c):
> >
> > /* TODO - big bad evil hack! */
> > /* uDAPL doesn't ever seem to keep track of ports with addresses. This
> > becomes a problem when we use dat_ep_query() to obtain a remote address
> > on an endpoint. In this case, both the DAT_PORT_QUAL and the sin_port
> > field in the DAT_SOCK_ADDR are 0, regardless of the actual port. This is
> > a problem when we have more than one uDAPL process per IA - these
> > processes will have exactly the same address, as the port is all
> > we have to differentiate who is who. Thus, our uDAPL EP -> BTL EP
> > matching algorithm will break down.
> >
> > So, we insert the port we used for our PSP into the DAT_SOCK_ADDR for
> > this IA. uDAPL then conveniently propagates this to where we need it.
> > */
> > ((struct sockaddr_in*)attr.ia_address_ptr)->sin_port = htons(port);
> > ((struct sockaddr_in*)&btl->udapl_addr.addr)->sin_port = htons(port);
> >
> > The OMPI code stuffs the port chosen by udapl for a listening endpoint
> > into the ia address memory (which is owned by the udapl layer btw).
> > There's a slight problem with that: The OFA udapl openib_cma code binds
> > cm_id's to this ia_address regularly. When an hca is opened, a cm_id is
> > bound to this address to obtain the local hca port number and gid that
> > is being used. In addition, a cm_id is bound to this address each time
> > an endpoint is created (either at ep_create time or ep_connect time).
> > So that ia_address field is used by the dapl cm to create local
> > cm_ids... Since the port was always zero, the rmda-cma would choose a
> > unique port for each cm_id bound to that address.
> >
> > But OMPI sets a the port field to non-zero, the rdma_cma fails all the
> > subsequent rdma_bind_addr() calls since the port is already in use.
> >
> > Perhaps this hack really is a workaround for a DAPL bug where somebodies
> > dapl wasn't tracking port numbers correctly?
>
> Yep. My memory is dim, but I think that was OFED's DAPL, or it was in
> the generic part of DAPL that all implementations seem to share.
>
> As hinted by the comment (I wrote it by the way), I think the best
> solution would be if dat_ep_query() returned the port number correctly.
> Most of uDAPL seems to just pass around pointers to internal data
> structures (which I'm not sure is the best idea in the world), so it
> didn't seem like a trivial fix to me at the time. I remember
> considering reporting this as a bug, but I didn't because the uDAPL
> standard didn't seem to enforce any requirements on passing the port
> number around with the address, so it technically wasn't wrong.
>
> Was the OFED uDAPL code switched from something else to RDMA CM at some
> point? I'm almost certain I was running fine on OFED's uDAPL at one
> point (in fact, a lot of the uDAPL BTL development I did was using the
> OFED stack).

Yes, the OFA uDAPL was changed from using the ib-cm to the rdma-cm a
while back. Perhaps you ran on the ib-cm version? And, the rdma-cma
started using port numbers and enforcing uniqueness even more recently I
think.

Perhaps Don Kerr has some insight on how the Sun uDAPL behaves? Should
OMPI still need this hack?

Steve.