[ofa-general] Default multicast group rate

[Hal Rosenstock]

Hi,

There has been a lot of discussion over the last week on failed
multicast joins.

The current default rate for multicast groups is 10 Gbps. This means
that slower nodes (whether due to 1x SDR equipment or a degraded link)
will fail the join.

The current default was chosen in the belief that most installations
would be 4x SDR equipment or better (the most common use case) rather
than the lowest common denominator use case. Also, choosing a lower
default affects preformance of all multicast groups (which includes the
IPv4 broadcast group as well as any other derived groups (not just IPoIB
multicast groups)). So when certain performance tests are run, this will
be a factor which needs to be investigated. The thinking was that those
subtle things are harder (but perhaps less frequent) to find than the
"harder" join error which forces the admin to decide one way or the
other so there is no masking this.

So the question is whether the best default is 2.5 Gbps which would
allow any nodes to join or whether the current default is appropriate ?
I know certain people's opinions who have been vocal on this list up to
now. I'm looking for other opinions. Thanks.

-- Hal