[openib-general] ipoib multicast timeouts

[Sean Hefty]

I have the kernel code for multicast support completed, and I'm trying to
migrate ipoib to use it.  So far, I see one main issue, and I'd like to verify
an approach to fix it.

The multicast module handles multiple join/leave requests to the same multicast
group.  Because multiple join requests can occur simultaneously, SA query
timeouts are controlled by module parameters.  Ipoib issues join requests with
an exponentially increasing timeout.

Some possibilities:

1. Do not migrate ipoib to use the multicast module.
2. Add a timeout to the multicast module.  It's not clear how to reconcile
different timeouts for the same group, so I'm less certain how to do this.
3. Currently, ipoib backoff is used both as the timeout for a single request and
the time between retries.  Instead, use it only the time between retrying
requests.

Thoughts?

- Sean