Re: [Qemu-devel] [RFC PATCH RDMA support v2: 4/6] initialize RDMA options when QEMU first runs on command-line

[Paolo Bonzini]

> On Tue, Feb 19, 2013 at 09:42:45AM +0100, Paolo Bonzini wrote:
> > Il 19/02/2013 07:00, Michael R. Hines ha scritto:
> > > Yes, this is done at migration time (see functions
> > > "rdma_client_init"
> > > and "rdma_server_prepare()")
> > > 
> > > To explain the host and port:
> > > 
> > > The separate host and port are used by the library "librdmacm".  This
> > > library performs a network translation between the IP address and a
> > > unique infiniband user-level Port number and the physical
> > > interface that has the RDMA capabilities. This library requires an
> > > IP address and port bound specifically to the requested RDMA interface
> > > to work.
> > > 
> > > The patch does not assume that the network interface used for TCP
> > > traffic will necessarily be the same as the interface used for
> > > RDMA traffic.
> > 
> > Of course the best thing to do would be to have all traffic on the
> > RDMA interface... :)
> 
> You can't do this with infiniband, RDMA is only possible once the
> connection is established.

Sorry, I meant on the infiniband interface.

Right now Michael (Hines)'s code needs two sockets, one for TCP and
one for RDMA.  If I understand correctly, the rdmacm library does not
need a separate address to set up the connection, that's just an
artifact of the implementation.

Whatever goes on in the TCP socket can be done on RDMA after establishing
the connection, or can be done with SEND.

Paolo

> 
> > > Alternatively, this host and port could be specified using the
> > > QMP
> > > "migrate" command, but this command already has the URI for the
> > > TCP side
> > > of things reserved.
> > > 
> > > If you guys like, we could specify a *second* URI on the QMP
> > > command
> > > line - we don't really have a preference.
> > > 
> > > Either way is fine........ whatever the consensus is.
> > > 
> > > - Michael
> > 
>