[ofa-general] [PATCH/RFC] IPoIB: Don't drop multicast packets sent before group is joined

[Christoph Lameter]

On Wed, 3 Jun 2009, Roland Dreier wrote:

> current net stack just drops packets during arp resolution, and IPoIB
> path resolution / multicast join is arguably the analogous thing.  So
> now I begin to wonder about Christoph's patch again.  With the old code
> we drop a lot of packets (potentially a lot more because of the
> unthrottled sender), but only during fabric events that cause multicast
> joins; but is delaying a lot of packets during a multicast join really
> better for actual apps?  Or are we better off dropping those packets we
> can't deliver in a timely way?

arps are a different thing from regular payloads. They are not handled
using socket semantics.

> Christoph, is this making a real app work better, or just making a
> multicast flood test case report better numbers?

It is necessary for a real app to work that was moved from 1G ethernet to
IB. Startup fails because of significant loss of multicast packets during
join.