[ofa-general] general questions about librdmacm

[Steven Dake]

On Fri, 2008-09-26 at 15:33 -0700, Roland Dreier wrote:
> > One more question and I'll get to experimenting.  Does this kernel
>  > module use "RDMA" and provide highest performance available for the
>  > application?
> 
> No, it is just using the IB adapter as a very fast NIC.
> 

Thanks so essentially to get RDMA support I'd have to use the RDMA
library.

> But you can't really use RDMA for multicast anyway.
> 
>  - R 

The RDMA library has features for joining a multicast group.  Could you
point me at the appropriate specifications about infiniband relating to
the limitations of RDMA when used with multicast (or hand me an
explanation would be fine too :)

Also to answer your questions about performance requirements: today
totem is entirely cpu bound when running on GIGE hardware with jumbo
frames.  A majority of this time I believe is spent copying message data
between kernel and userspace, and then the other copies that take place
around the protocol.  I'd like to remove any copies that are present if
possible to give the CPU more bandwidth to execute the protocol.

Thanks Roland

Regards
-steve