[ofa-general] Re: multicast join failed for...

[Michael S. Tsirkin]

> Quoting Hal Rosenstock <halr at voltaire.com>:
> Subject: Re: multicast join failed for...
> 
> On Wed, 2007-04-11 at 15:47, Michael S. Tsirkin wrote:
> > > Quoting Hal Rosenstock <halr at voltaire.com>:
> > > Subject: Re: multicast join failed for...
> > > 
> > > On Wed, 2007-04-11 at 14:12, Michael S. Tsirkin wrote:
> > > > > > If yes, I'm actually not too happy with this.
> > > > > > 
> > > > > > Would something like the following heuristic work better?
> > > > > > - select the max rate between all participants
> > > > > 
> > > > > The issue is that one doesn't know all the participants in a group as
> > > > > they are joined dynamically.
> > > > > 
> > > > > (I think we've been over this aspect on the list several times in the
> > > > > past.)
> > > > 
> > > > That's why I suggest the fix, so that the rate is adapted
> > > > dynamically.
> > > > 
> > > > > > - when a host with lower rate joins, destroy the group
> > > > > 
> > > > > I don't think a group can be destroyed like this "underneath" its
> > > > > existing members.
> > > > > 
> > > > 
> > > > Of course it can. That's what happens when SM is restarted.
> > > 
> > > Client reregistration ? I don't like using that big hammer as a solution
> > > to this. Seems a little harsh to me.
> > 
> > I think it's not too bad
> 
> It requires all subscriptions to reregister. This affects more things
> than just multicast or even the groups affected which might not be all
> of the multicast groups. Hence BIG hammer.

Changing an option in opensm config requires restarting
opensm. Isn't that right? So its an even bigger hammer.

> There could be a more
> graceful way to deal with this. I don't like using client reregister
> unless absolutely needed.

What are the other options that have the same funcitionality?

> >  - previously we had some client failing join
> > which is worse.
> 
> Maybe not. Maybe that's what the admin wants (to keep the higher rate
> rather than degrade the group due to some link issue).

Rate could be an option, but I think generally people prefer
things working even if at a slower rate.
Wat does opensm do now?
I think it uses the max possible rate when group is created.
Is that so?

> >  And we can still keep an option to limit the rate
> > manually.
> > 
> > > I'm not convinced it's even
> > > required either,
> > 
> > How do you mean? All end-points must know the rate is now lower.
> 
> I didn't think we had the complete story yet on what is going on.

You are speaking about a specific instance then?
OK, but I'm speaking generally, the issue comes up
quite often.

-- 
MST