[openib-general] First Multicast Leave disconnects all other clients

[Hal Rosenstock]

On Thu, 2005-12-01 at 01:07, Eitan Zahavi wrote:
> > >
> > > The bottom line:
> > > We are missing 3 agents in the OpenIB stack:
> > > InformInfo - handling registrations and Report dispatching
> > 
> > These are not currently used.
> [EZ] They are by SRP initiator.

Not the SRP initiator in OpenIB svn as far as I can tell.

> > > ServiceRecord - tracks registrations
> > 
> > ServiceRecord is implemented in sa_query (and was used by AT/uAT but
> > that is largely historical now)
> > 
> > > Multicast Join/Leave - tracking registrations to multicast groups
> and
> > > ref-counting
> > >
> > > All these agents should be able to cleanup dead client registrations
> and
> > > also provide re-registration in case of SM ClientReregistration
> event.
> > 
> > In OpenIB, any Set of PortInfo (which includes ClientReregister)
> > currently causes a (coarse) event (LID change) which causes IPoIB
> client
> > to reregister its multicasts registrations with the SA.
> > 
> > > Please see below
> > > > >
> > > > > It seems the IBTA intent was that the IB driver will be
> responsible
> > > for maintaining
> > > > the list of clients
> > > > > registered to each group.
> > > >
> > > > Yes, the end node is responsible for tracking the registrations
> within
> > > > the node and fabricating responses when the node does not want to
> > > leave.
> > > > Is delete a different case though ?
> > > [EZ] No it is not. Delete of multicast group is really the last
> leave.
> > 
> > There is an explicit delete. While it shouldn't be needed to be
> forced,
> > there is always some scenario where this is useful.
> [EZ] To my best knowledge any leave is a "delete" so there is no way for
> any client to force other members out of a group. It can only leave
> itself. The delete will happen when the last will leave.

Yes, you are right, other than the last full member (join state) rule.

> > > > > But the IB core does not track what clients registered (through
> SA
> > > requests) to a
> > > > particular multicast group.
> > > > > The first client to leave the group causes the rest (of the
> clients)
> > > to be disconnected.
> > > >
> > > > This is an implementation issue IMO and applies to other
> subscriptions
> > > > too (not just limited to multicast).
> > > [EZ] I agree it is an implementation issue. I hope it will get
> > > implemented in OpenIB.
> > 
> > It will. It's a question of priorities and timing.
> > 
> > > > > My proposal is to provide an API for such registrations at both
> user
> > > and kernel and
> > > > track the requesting processes.
> > > > > Cleanup is also required both by process and kernel module
> > > granularity.
> > > >
> > > > Is the API the SA client request itself for this ? Shouldn't the
> > > > tracking be done there (within sa_query.c) ?
> > > [EZ] It will be hard to sniff the MADs (especially user level) for
> all
> > > the registration flows.
> > 
> > It's not the sniffing which is hard but perhaps identifying which
> client
> > (and reference counting).
> > 
> > > So I propose we should have
> > >
> ib_join/ib_leave/ib_reg_svc/ib_unreg_svc/ib_reg_inform/ib_unreg_inform.
> > > Both in user land and in kernel.
> > 
> > I think this is TBD and the API would be discussed on this list first
> > prior to any implementation.
> > 
> > > > > BTW: The same API could also handle "Client Reregistration" for
> > > multicast groups,
> > > >
> > > > Client reregistration is for all subscriptions (including
> > > ServiceRecords
> > > > and events as well).
> > > [EZ] Yes exactly. I believe similar problem exists for all
> > > registrations.
> > > >
> > > > > such that we could avoid the need to have that code duplicated
> by
> > > every client.
> > > >
> > > > I'm missing how client reregistration would help here. Can you
> > > elaborate
> > > > ?
> > > [EZ] It is related to the reference tracking:
> > > If a kernel module tracks all registrations to refcount them and
> perform
> > > cleanup, it could with similar effort also send the -
> re-registration in
> > > the event of SM change ...
> > 
> > Sure, there are multiple ways to skin the same cat.
> > 
> > > >
> > > > > But this refers to yet another API that is missing: Report
> > > dispatching which deserves
> > > > its own
> > > > > mail...
> > > >
> > > > I'm missing the connection between reregistration and report
> > > > dispatching.
> > > [EZ] Sorry for not being verbose. The need for Events dispatcher is
> > > based on the fact that only one client should respond to Report with
> > > ReportRepress. Reports are "unsolicited" MADs coming into the
> device. In
> > > umad the implementation prevents any "multiple" client registration
> for
> > > receiving any "unsolicited" MAD - only one class-agent needs to be
> there
> > > handling "unsolicited" messages. This is fine - but what it means is
> > > that when two clients wants to be notified about events they should
> > > register with that agent and the agent should be able to dispatch
> the
> > > message to all registered clients as well as send only one response
> > > back.
> > 
> > Wouldn't report represses be reference counted and only actually sent
> on
> > the wire when all subscribed clients within the node indicated repress
> ?
> [EZ] As you say there are many ways to skin a cat. I am not sure we need
> to wait for all clients as they are located on the same node and will be
> surely notified.

Right, it just needs to be done once whether it was actually delivered
to any client, clients, or none at all.

-- Hal