Fwd: Re: [openib-general] static LID computationwithTS_HOST_DRIVER

[Michael Krause]

At 07:48 PM 9/29/2004, Roland Dreier wrote:
>     Yaron> While I agree that other SM's in a recovery/merge phase
>     Yaron> should try and preserve the LID's I think a CA shouldn't
>     Yaron> just like it is not supposed to change its own P_Key table,
>
>I don't think the P_Key table is a good analogy.  There is a very
>clear statement in the IB spec for what values should be in the P_Key
>table before the SM sets it.  I don't know of any such statement for
>PortInfo:LID.
>
>     Yaron> But any way out of curiosity how do you generate a unique
>     Yaron> LID (locally by the host) for every node in the fabric in a
>     Yaron> large fabric when the ports are down and the nodes don't
>     Yaron> talk to each other ? (I hope not through Ethernet :))
>
>     Yaron> Or how do you anticipate the LMC value (LID spacing)?
>
>If the application cares about this, the administrator has to set
>things up so that it can work.
>
>Of course there are scenarios where this breaks.  It's up to the user
>to avoid them if it matters.

The whole point of a central management scheme was to simplify the 
management of the fabric and enable one to scale a solution across a large 
number of endnodes.  A LID defines a path in the fabric not just an 
endnode.  The LMC defines a range of LID assigned to a port and thus the 
number of paths supported within the fabric.  This allows traffic to be 
routed through the fabric to meet specific QoS objectives or to avoid 
congestion on a given path under varying workloads.  Attempting to just 
assign this at the endnode is simply wrong and certainly goes against the 
intention of the IBTA.

If really want a static LID and its only purpose is loopback, then do this 
within the CI and don't mess with the port configuration.  It is cleaner 
and will make life easier for the customers as there will not be 
conflicting policies nor a requirement that the customer has to know every 
nuance of a particular implementation.  The goal is supposed to make IB 
easier to deploy for customers and not require them to be experts at all 
aspect of IB operation.

Mike 
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