[openib-general] [PATCH] expand local SA cache to include all path records from source

[Sean Hefty]

Hal Rosenstock wrote:
> As the end node cannot know the policies the SM used for routing, etc.,
> path records are insufficient in terms of some of the interesting
> characteristics for filtering like path independence (as fault
> independent as possible). 

This patch doesn't handle policy.  It only stores multiple path records.

Also, it seems like the argument can go both ways here.  The SM doesn't know the 
policies of the applications or their traffic patterns.  A distributed 
application may want paths from nodes A to B to have path independence from 
paths from nodes C to D.  Can the SM handle such requests?

> There's also a 1.2 erratum which enhances SA MultiPathRecord to support
> scoping of S/DGIDs. It supports explicit, same node, same system with
> and without high availability (separate HCAs). That could also be used
> when supported by the SA.

It shouldn't be hard to change the path query from GetTable to GetMulti, once 
the MAD layer supports dual-RMPP.

> The API looks fine to me. One thing to note is to keep an eye on the
> lookups done on the local database and possibly optimizing them if
> needed.

Tracking path usage becomes difficult, and would likely require involving the 
CM, and possibly address handle creation (for UD QPs that didn't use SIDR). 
When the cache is updated, checks would need to be added to see if a path is 
currently in the cache, and invalid paths would need to be removed.  There would 
be a lot of additional work needed to do this.

- Sean