[ofa-general] [PATCH] rds: use separate ports for TCP and IB

[Olaf Kirch]

On Tuesday 03 June 2008 15:21:35 Talpey, Thomas wrote:
> >This may also become a problem for RDS, but in a different sense.
> >If you bind an RDS socket to a specific IP address, this also selects
> >a transport. If you bind to an IP address owned by ib0, you select
> >the IB transport. If you bind to an IP address owned by say eth0, you
> >select the TCP transport.
> 
> I think this is a bit of an overloading, and will lead to issues down the road.
> IP addresses really aren't about interfaces, they're about hosts. For example,
> on TCP (etc), hosts will respond to any of their IP addresses on any of their
> interfaces (IP routing often depends on this). I suspect it would be better to
> make the transport selection explicit. IPv4/IPv6 selection may fall into the
> same issue later.

I assume the reason for doing it in this way is "historical", IOW
the Oracle IPC layer expects things to work this way :-) But I agree
it could be done better. In general, you shouldn't need to bind to
any specific transport at all, you can make the decision on the fly
by doing an IP flow lookup - and then you can look at the device to
decide whether you're on TCP, IB, iWARP, whatever.

> >I think for now it's okay to default to iWARP and punt if the remote
> >doesn't support it. But in the long run this is something that needs
> >to be addressed - either in RDS, or in the way ofed handles iWARP NICs.
> 
> Here I think you've made an even bigger assumption - that not only does
> your interface support iWARP, you're assuming the peer's does too! But

Yes, I'm aware of that assumption.

> Is RDS able to use MPA negotiation to mutually agree to enable RDMA?

We could certainly modify RDS over TCP to include some kind of
negotiation. RDS/IB also exchanges some information when the connection
is established, and it helps in setting up things (eg the decision
whether to use congestion control is based on this "negotiation").

Olaf
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